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Tsarnaev Trial

For Further Study:

The Tsarnaev Trial and The Impact of Video Evidence

Compiled by Alex Gutierrez, Carolina Morales, and Ryohei Tsukuda

I. Introduction

     The Boston Marathon bombing occurred in an area of downtown Boston that was surrounded by shops, businesses and other key venues.  After the tragedy and during the ensuing manhunt, national security agencies that included the National Counterterrorism Center, FBI, CIA, ATF, NSA and DEA began a collection of weeks worth of video evidence from the area.  The dragnet involved collecting evidence from public video surveillance cameras and other sources that ranged from traffic cameras, security cameras from private businesses and security systems.  As the manhunt for the bombers continued, various videos depicting the suspects were found and disseminated, ultimately leading to the identification of Dhozokar Tsarnaev and Tamerlan Tsarnaev as the perpetrators.

     The role of video evidence not only played a decisive role in capturing Tsarnaev, but will also play a key role in his conviction.  This page seeks to review various experiments that investigate the impact of video evidence upon the jury’s decision-making process.

II. The CSI Effect and High Juror Expectations

     Due to the popularity of crime-solving tv shows such as CSI: Miami and Law and Order, there has been an overall increase in the public’s awareness of scientific evidence.  Although these shows may encourage public awareness of the scientific method, they may have fostered unrealistic expectations and a false sense of expertise in interpreting scientific evidence in jurors, which in turn may have troubling effects on jury-decision making. This factor in jury decision-making has been coined as the “CSI Effect.”  According to some observers, juries have come to expect unrealistic standards for scientific evidence.

     As Andrew Thomas describes in The CSI Effect: Fact or Fiction,i the presence of the CSI can create bias in the jury that has an impact on jury decision-making.  In an extensive survey of Maricopa County prosecuting attorneys, Thomas found that 8 out of 10 prosecutors believe that jurors are disappointed with the lack of forensic evidence presented at trial.ii  Moreover, 72% of prosecutors surveyed believed that jurors maintained a false sense of expertise with regard to understanding forensic evidence.iii  Critically, almost half of the prosecutors surveyed (45%) believed that juries relied too heavily on scientific evidence at the expense of other evidence such as witness testimony.iv  Although this survey is limited to the impressions of prosecuting attorneys, a recent study found that CSI viewers have higher expectations for scientific evidence.v Ultimately, these studies reinforce the critical role that scientific evidence plays in the decision-making process of the American jury and the high expectations that juries have for evidence presented at trial. 

III. Understanding the Impact of Video Evidence on Jury Decision-making

A. The Role of Video Quality and Video Framing on Jury Decision Making

     Although the substance of video evidence is usually perceived as a form of evidence that is often devoid of human error such as memory loss and perception-based inaccuracies, the human element can still have an influential role in the perception of video evidence by the jury.  First, we sought to evaluate the impact that seemingly incidental factors such as video size, video quality, video size and video framing can have on jury decision-making processes.

     One study conducted by Heath and Grannemann examined whether video image size alters how other trial components are  The study analyzed how opinions of a defendant, are influenced by the size of a video image.  A total of 263 undergrads were examined from a small, northeastern university and their ages ranged from 18-50 with a median age of 20 ½.  Approximately 79% were white, 10% were African American, 5% were Asian, 3% were Hispanic, less than 1% were Native American, and 3% were other.  Participants were presented with a case and trial summary about a female defendant charged with killing either her spouse or an unfamiliar person. Participants were also given information that included either unsubstantial or convincing evidence against the defendant. Participants were then presented with a video clip of a woman giving a “part of the defendant’s testimony.”  The words in each video were identical but the emotion level was either low or intermediate.  The defendant in the low emotion scenario showed little emotion, while in the intermediate emotion scenario, the defendant displayed verbal and nonverbal behavior indicating sadness.  The video was presented on either a large 27’’ television screen or on a 9’’ screen.  After watching the video clip of the defendant testify, participants answered a questionnaire. The results found that convincing evidence was perceived as stronger and unsubstantial evidence was seen as weaker when participants viewed a large screen instead of a small screen.

From: Wendy P.  Heath and Bruce D. Grannemann, How Video Image Size Interacts with Evidence Strength, Defendant Emotion, and the Defendant-Victim Relationship to Alter Perceptions of the Defendant, Behav. Sci. Law 32:496-507 (2014).

From: Wendy P.  Heath and Bruce D. Grannemann, How Video Image Size Interacts with Evidence Strength, Defendant Emotion, and the Defendant-Victim Relationship to Alter Perceptions of the Defendant, Behav. Sci. Law 32:496-507 (2014).

     An analysis was done to examine the effects of emotion level, defendant/victim relationship, evidence strength and video image size on the participants’ verdicts.  Evidence strength influenced decisions.  When evidence was weak only 23% thought the defendant was guilty; when evidence was convincing, 58% thought the defendant was guilty.  The closeness in relationship between the defendant and victim also affected verdict decisions with people being more apt to say the defendant was guilty when she had been accused of killing her spouse (46% guilty) in comparison to an unfamiliar individual (35% guilty).  Additionally, when the participants had observed the defendant on a large screen and had read about the strong evidence against her, 65% saw her as guilty while only 52% saw this defendant as guilty when the video screen was small.  Similarly, when the strength of the evidence was weak, and the defendant was viewed on a large screen, only 13% saw the defendant as guilty as opposed to 32% who saw this defendant as guilty after viewing her on a small screen.

     When the image was large, verdict certainty remained high.  But, when the image was small and the defendant showed less emotion, viewers were less certain of their verdicts.

     The relationship between the defendant and the victim impacted the defendant’s level of guilt (guilt was rated on an 11-point scale with higher numbers indicating more guilt).  The defendant was given a higher guilt rating when her spouse was the victim (Mean = 5.73) as opposed to an unknown person (Mean = 4.87).  In addition, the defendant was given a higher guilt rating when the evidence was convincing (Mean = 6.39) rather than unsubstantial (Mean = 4.20).  When evidence was convincing, the size of the video image had little impact (guilt ratings were high in both cases), but when the evidence was weak, the defendant was seen as more guilty when the video image was small as opposed to large (large image and strong evidence: Mean = 6.48; large image and weak evidence: Mean = 3.62; small image and strong evidence: Mean = 6.30; small image and weak evidence: Mean = 4.74). Participants gave shorter sentences to the defendant on a large screen (Mean = 28.78 years) versus a small screen (Mean = 32.72 years).

     The defendant was rated as having less credibility when the evidence was convincing (Mean = 5.10) rather than unsubstantial (Mean = 6.45).  There was also an interaction between relationship type, emotion level and image size.  Specifically, the defendant on the small screen who didn’t show much emotion after being charged with killing her husband was seen as having the least amount of credibility.  Her credibility increased greatly when she was viewed on a large screen (see Figure 1).

     Video image size had a large impact on the jury’s decision-making as an increase in video size amounted to strong evidence seeming stronger and weak evidence seeming weaker.  This result is seen prominently when participants rendered their verdicts.  When the video was large rather than small, the defendant was less likely to be found guilty when evidence was weak, and more likely to be found guilty when evidence was strong.  An increase in the video image size heightened the effects of evidence strength.

     Participants also gave shorter sentences to the defendant presented on a large rather than a small screen.  With regard to guilt, the defendant was seen as highly guilty when evidence was strong with the highest guilt ratings resulting from a large image presentation, but when evidence was weak and the presentation was on a large as opposed to a small screen, the defendant was seen as less guilty.  This result is in line with the conclusion of Detenber and Reeves (1996) that bigger image sizes can “intensify viewers’ evaluations of content.”

     Participants were most certain of their verdict when the defendant showed little emotion and this little emotion was projected on a large screen.  The bigger screens seemed to allow participants to be able to see what little emotion there was there better and bigger screens also can make information more dynamic and easy to remember and can influence jurors.

     Some potential limitations of this research are that it only examines how people see a female defendant, and females are stereotypically more emotional than men. Thus, including a male defendant in the study on image study could change the jurors’ views of this defendant.  Lastly, there is a limitation related to external validity; videotaped stimuli were given to college students, but this scenario might not be similar enough to a real juror experience.

     This study shows that video image size can affect jury decision-making and trial outcome variables such as guilt determination and sentencing, and non-trial outcome variables that could affect jurors’ decision-making such as defendant credibility.  As a result, attorneys should consider carefully how to present visual evidence to jurors, taking into account whether the evidence is strong or weak.

     A study by Fishfader, Howells, Katz, and Teresiexamines video re-creation, which is where actors reenact events relevant to the case.vii  Some argue that the use of video re-creations is an attempt to change the emotional state of the jury while giving facts.  This study also examines whether the format of evidence presentation creates differences in emotionality and retention levels. A total of 102 mock jurors reviewed case materials from a wrongful death suit in either print through transcripts, videotaped oral testimony, or videotaped testimony plus video re-creation. Variation in emotions was assessed with the Profile of Mood States questionnaire. Retention levels of factual information were measured by a multiple choice questionnaire and through the participants being asked to calculate damage awards as well as liability levels of both the plaintiff and defendant in the case. The hypothesis of the study was that jurors who read the transcripts would hold more information than those who watched video content and that participants in the videotaped testimony plus video re-creation condition would give higher damages to the defendant and find more liability on the part of the plaintiff than those who read transcripts because of the higher level of emotion and impact in video content.

     The results found that the jurors in the videotaped testimony conditions did experience higher emotions than those who read transcripts and that these higher levels of emotion led to lower liability findings for the plaintiff but there was no difference in damage calculations.  This study suggests that while interpretations of levels of defendant liability are affected by emotions, damage awards can be highly variable and thus might show differing damage awards.  Another limitation of this study is external validity; it used mock jurors rather than real jurors. This study is relevant to jury decision-making because simply based on whether or not attorneys present evidence in a videotaped format rather than a transcript format, jurors' decision-making as to whether a defendant is guilty or innocent can be skewed based on the greater exposure to emotion and the more arresting content in videos.

From: Vicki L. Fishfader, Gary N. Howells, Roger C. Katz, and Pamela S. Teresi, Evidential and Extralegal Factors in Juror Decisions: Presentation Mode, Retention, and Level of Emotionality, 20 Law and Human Behavior  565, 596 (1996).

     Another study by Ellison and Munro explores the findings of a study in which 106 volunteer members of the public observed one of four mini rape trial reconstructions and were asked to deliberate as a group towards a verdict.viii The study examined how opinions of adult rape testimony are shaped by different types of presentation, including video recorded evidence. This study explored the effect that the following have on mock jurors; (1) live-links; (2) video recorded evidence in chief followed by live link cross-examination and (3) protective screens. The results found that there was no significant effect of these differing presentation modes, suggesting that concerns over the use of special measures by adult rape complainants may be over-warranted.  The results of this study matter and implicate jury decision-making because unlike the previous study where it was found that video content in contrast to transcripts elicited more emotion from jurors and skewed their decision-making, this study indicated that differing types of presentation for evidence within the realm of video does not make much of a difference in jury decision-making. Some limitations of this study are that the sample size could potentially be too small to apply to the general population as the study involved only 160 participants and there is the limitation of external validity; there were mock jurors involved and there is a lot of unpredictability in regards to the emotional reactions that survivors of sexual assault have.

     Another study by Heath, Grannemann and Peacock examines two experiments that were conducted to examine the effects of a defendant’s emotional level during testimony on mock jurors’ decisions.ix  In Experiment 1, the defendant’s level of emotion (low, moderate, high) and mode of presentation (audio, video) were wide-ranging.  The defendant that showed a low level of emotion, as opposed to a high level of emotion, was seen as more guilty and less credible. In regards to jury decision-making, this finding is important because it shows that simply by a defendant exhibiting more emotion in trial the jury can skew their decision-making in favor of the defendant and find the defendant less guilty and more qualified. In Experiment 2, using only the video mode, emotion level and evidence strength (strong, weak) were varied.  A defendant’s emotional level tended to affect jurors’ decisions only when the evidence against the defendant was weak.  This finding also implicates jury decision-making and tempers the finding in study 1 by suggesting that a jury’s decision-making will be skewed in favor of the more emotional defendant and in finding that defendant competent and innocent only if the evidence against the defendant is tenuous to begin with. The limitations in this study are that the emotions investigated here are levels of emotional distress and sadness rather than positive emotions and that it examined a woman’s emotions in the courtroom rather than a man’s.  Another limitation in this study is that the defendants in the case were college students rather than actual jurors and the students made decisions on their own rather than deliberating in groups, which is essential to the jury experience.

     Lastly, a study conducted by Feigenson discussed two other studies in which the presence or absence of video evidence was changed as an independent variable.x  In the first study, a crime scene walk-through was used and in the second study, a video re-enactment of an accident was used. The video reenactment didn’t change participants’ verdicts, on one hand, or on the percentage of liability that they gave to the plaintiff or their damage calculations. This study referenced the results from earlier studies where it was found that presenting testimony on videotape rather than live, did not affect mock jurors’ verdict preferences.  Mock jurors who saw a criminal suspect’s videotaped confession in which only the suspect was seen on screen were more likely than those who also saw the interrogator to believe that the confession was voluntary and that the suspect was guilty.  Additionally, mock jurors who watched a criminal suspect’s videotaped confession in which only the suspect appeared on screen were significantly likelier than those who also saw the interrogator to believe that the confession was voluntary and that the suspect was guilty.  Another study examined how mock jurors who saw an animation of a slip and fall accident found the expert witness whose testimony the animation showed to be more credible than did those who saw still slides or no visuals.  The findings from these studies indicate that while some studies found that video reenactment did not change jurors’ verdicts or damage calculations, other studies found that jurors are affected by whether or not they see videotaped evidence and find that watching videotaped content of solely the suspect can lead jury members to believe that the suspect is guilty. Additionally, when jurors see video content from an expert witness, this leads them to believe that the witness is more persuasive than expert witness testimony that does not include visuals. The limitations of this study are external validity; the participants are not representative of real jurors, and there is an absence of deliberations.

B. Video Evidence and Pre-existing Jury Bias

     Although it would be ideal for jurors to divide their personal bias from their decision-making processes especially in relation to video evidence, there is evidence that the opposite happens when presented with ambiguous video evidence.  Specifically, this section seeks to uncover what happens when a jury is presented with ambiguous video evidence.  Do jurors place lower value on ambiguous video evidence due to its limited informative content or does ambiguous video evidence invite the juror to make assumptions that implicate their pre-trial bias?   As professors Balcetis, Granot, Schneider and Tyler found in their study, “Justice is Not Blind: Visual Attention Exaggerates Effects of Group Identification on Legal Punishment,” the role of pre-trial bias can have a significant role in altering the way that potential jurors make decisions.xi


     Balcetis, Granot, Schneider and Tyler argue that visual attention to a particular member of an in-group or out-group can affect jury decision-making by essentially priming group bias through visual identification with individuals in video evidence.  Group bias is the identification of a person within a group, essentially demonstrating preference for a group of people that they are similar to and bias against others who are not members of their group (or who are dissimilar to their own characteristics).  In essence, they argue that jurors are more likely to punish individuals who are not like them and less likely to punish individuals who are more like them.  Although this study has a broad scope in cognitive psychology, it is crucial to note that the study focused upon video evidence that was intentionally ambiguous in order to measure the extent to which the participant’s pre-trial bias played a role in their interpretation of the video and the legal punishment that they would ultimately give each actor.

     This experiment was conducted in 3 main studies.

Study 1


     The first study measured pre-trial bias by subjecting 152 NYU undergraduate students to a survey that determined the degree to which they identified with police on a 7-point scale from strong disagreement to weak disagreement using questions such as, “If you talked to most police officers, you think that you would find that they have similar views to your own on many issues” and “your background is similar to that of most police officers.” The participants were tested again with a 20-question survey that measured their identification with police on a 9-point scale.

Ambiguous Video Evidence Data Gathering

     The participants then watched a 45 second video that contained an incident in which an officer struggled with a suspect, but it was not clear as to who had initiated the first punch. Critically, it was ambiguous as to who the initial aggressor was.  Participants then watched a video depicting a clearly unjustified use of foce in which an officer slams a suspect against a car and a fence while the suspect’s hands are up.  The participants then watched a third video that depicted a clearly justified use of force in which the civilian was the first aggressor.  The order in which participants viewed the videos was randomized.

Unambiguous Video Evidence Data Gathering

     After watching each video, the participants were asked to determine to what extent the officer’s actions were incriminating.   Specifically, they reported to what extent they believed that the officer initiated contact on a 7-point scale (ranging from strongly disagreeing that the officer initiated to strongly agreeing that the officer initiated).  The participants were also asked to what extent they believed that the officer was justified in using force against the civilian, searching the civilian, touching the civilian and using handcuffs.  Lastly, the participants were asked to rank on a 7-point scale the degree to which they believed that the officer should be reprimanded and punished.


     The researchers used linear regression to plot the survey scores of the participants. The participant’s previous survey results (measuring their identification with the police) were compared with their survey results regarding their views on the justifiability of the officer’s use of force in the ambiguous video.  Researchers found that participants who focused their attention on the officer for a long amount of time and weakly identified with the police believed that the officer deserved harsher punishment.  Similarly, those who focused their attention on the police officer and identified strongly with the police supported the officer’s actions.  In order to rule out the potential confounding factor that participants were making punishment decisions based upon their relationship with authority and political leanings, the justifiability survey results and identification survey were compared to the political views survey.  Through linear regression, the researchers found that while there was a correlation between the participant’s identification with police and their punishment results.  Specifically, participants were more likely to punish the police office in the ambiguous video if they did not associate with the police in their pre-experiment survey and less likely to punish the police officer if they highly associated themselves with the police or viewed the police in a more positive light.  This is significant because the ambiguous video essentially polarized the participant’s punishment along the lines of their pre-experiment bias. 

     As shown on graphs A and B (taken from the experiment itself), the more visual fixations that the participants had on the police officer (the more that they focused upon the officer) correlated with a punishment that ultimately aligned with their identification with the police.

From: Yael Granot et at., Justice is Not Blind: Visual Attention Exaggerates Effects of Group Identification on Legal Punishment. 143(6) J. of Exp’l. Psychol.: Gen. 2196, 2201 (2014).

From: Yael Granot et at., Justice is Not Blind: Visual Attention Exaggerates Effects of Group Identification on Legal Punishment. 143(6) J. of Exp’l. Psychol.: Gen. 2196, 2201 (2014).

Study 2

     The researchers then conducted a second study that mirrored the first study and differed only in that the participants were specifically asked to focus their attention on either the civilian or the police officer.  The participants were grouped into two equally numbered groups, one that focused their attention toward the police office and another that focused its attention on the civilian.  Specifically, the participants watched a different 35-second ambiguous video that showed a police officer that was involved in an altercation with a civilian.  It was unclear and ambiguous as to who initiated the aggression.   


     As shown on graph B, the researchers found that those who were asked to fixate their vision (focus on) the police officer assigned punishment to the officer in line with their previous identification with the police officer.  This study reinforced the findings of the first study, affirming a participant’s visual focus upon the officer in an ambiguous altercation prompts the participant to punish the officer in a manner consistent with their identification with the officer and their pre-trial bias.

Study 3
     In order to branch out from the police-civilian context, the researchers conducted a third study to measure the role of in-group and out-group bias (the extent to which an individual identifies with a certain group) in terms of assigning punishment after viewing a video in which assigning fault was ambiguous.


     The participants (103 NYU undergraduates, specifically: 18 men/ 42 non-minorities) were given a fake personality survey that ultimately categorized the participants as either belonging to a “blue” personality group or a “green” personality group based on random assignment.  The participants then watched a 48-second muted video in which two white, college-aged males were shown fighting.  The participants were told the males were actually participants in the study and that one was a “blue” member and the other was a “green” member.  The males wore colored shirts that reflected their affiliation.  Participants were then asked to make judgments on a 7-point scale (ranging from strongly disagree to strongly agree) to determine the extent to which they believed the parties were at fault.


     Consistent with previous studies, participants who focused their attention on the out-group individual, the male who was not in their identification group of “blue” or “green” were more likely to dole out harsher punishment and attribute blame to that individual.  As demonstrated through the previous studies, the participants attributed blame based upon their group affiliation when they focused their attention to the out-group individual. 

Shortcomings in Experiment Design


     The participants were all undergraduate students.  Although NYU students may be a bright group, the age group does not represent the public as a whole.  It may be convenient and easier to use undergraduates as subjects, but there are fundamental issues with external validity that require the researcher to make a critical jump from test subject to potential juror.  Ultimately, this issue does not ultimately render the study’s result unusable because the role of in-group and out-group bias tends to cross all ages and socioeconomic backgrounds.  However, these results must be taken with a grain of salt as the sample is not completely representative of American juries as a whole.

Conclusions: The Polarizing Effect of Ambiguous Video Evidence

     Although conclusive video evidence would be ideal it is not always available. This study reveals a crucial response that jurors have to ambiguous video evidence.  Although one would hope that jurors avoid making assumptions when reviewing evidence that is not entirely clear, this study demonstrates that the opposite is true.  Jurors are more likely to assign guilt based upon their pre-trial bias when presented with ambiguous video evidence.  This is relevant to the Tsarnaev trial because the Tsarnaev trial has a degree of uncertainty with relation to the level of mens rea that is attributable to Dzohokar Tsarnaev.  Although the video evidence clearly shows Tsarnaev at the scene of the crime with his brother and carrying a backpack, there has not been any video evidence presented that shows Tsarnaev actually laying the explosive.  While Tsarnaev admits guilt in his participation of the crime, he contends that his willingness to commit the crime did not come of his own volition, but as a result of a manipulative brother.  The implications of this study when combined with the somewhat ambiguous evidence presented to the jury could prime pre-trial bias in the jury based on the disassociation effect of out-group bias.  Ultimately, this can have a deleterious effect on jury decisions because the priming of pre-trial bias through the use of ambiguous video evidence can hamper the impartial role of the jury.

The Impact of Graphical Gruesome Evidence on Jury Decision Making

1. Introduction
     Video recording evidence in Tsarnaev trial, which includes bombing scene and injured victim, can be classified as “gruesome” evidence which could cause emotional reaction in viewers and have unfavorable impact for the defendant on jury decision-making.
     To investigate what effects these graphical items will occur, first, we would review several mock juror studies about graphic gruesome evidence. Two studies are about civil cases [(a), (b)] and four studies [(c), (d), (e), (f)] are about criminal cases. Gruesome evidence studied here includes color photographs [(a), (b), (d), (e), (f)], black and white photographs [(b), (d)], and video recordings [(c)]. Studies were conducted in the U.S.[(a), (b), (c)], Canada [(d)], Australia [(e)], and Japan [(f)]. Second, we briefly analyze what can be said from these studies and the limitations of these studies. We also discuss possible strategies which the defense attorney can use to avoid/reduce the impact of gruesome evidence.

2. Brief Summaries of Studies

(1) Studies about Civil Cases

(a) Oliver, E. & Griffitt, W. (1976). Emotional arousal and “objective” judgment. Bulletin of the Psychonomic Society, 8, 399-400. (US)

     Subjects were 48 students from introductory psychology classes at Kansas State University, that read a brief written summary of a personal injury case in which a farmer was allegedly injured in his hand because the owner of the farm improperly maintained equipment of the farm. Half of the students saw four color-slides of a badly injured hand. The other half did not see any slide. Each subject answered questions without deliberation. The subjects who saw the slides were likely to award higher monetary damages.

 (b) Whalen, D. H., & Blanchard, F. A. (1982). Effects of photographic evidence on mock juror judgement. Journal of Applied Social Psychology, 12, 30-41. (US)

     Subjects were 144 female undergraduate students, that read a three-page written description of a civil action in which 10-year-old boy was allegedly injured in an abandoned building because the owner did not constructed sufficient barriers to entry the building. Case description varied in two points: [1] Blameworthiness of the defendant and [2] Severity of injury. Each subject saw, (a) 8x10 inch color photograph of injured child, (b) 8x10 inch black and white photograph of injured child, or (c) no photograph. Each subject answered questions without deliberation. The results of this study are complicated and it is difficult to say simply what kind of impact the photographs caused.

(2) Studies about Criminal Cases

(c) Kassin, S. M., & Garfield, D. A. (1991). Blood and guts: General and trial specific effects of videotaped crime scenes on mock jurors. Journal of Applied Social Psychology, 21, 1456-1472. (US)

      Subjects were 48 students (24 male, 24 female). All subjects were randomly assigned to one of three groups: [1] Relevant videotape, [2] Non-relevant videotape or [3] No-videotape control. Each subject read a 49-page transcript of a murder case and filled out a 4-page questionnaire without deliberation. Before reading the transcript, relevant videotape group watched 1-minute tape of the actual scene of crime (the camera focused on the victim’s body after the murder) which is discussed in the transcript; non-relevant videotape group watched the same videotape but were explained that the videotape was irrelevant to the crime which is discussed in the transcript; no-videotape control group did not watch any videotape.

      Conviction rate was low regardless of the group the subjects belonged to. The author suggests that this result could be due to extreme weakness of the prosecution’s case. There was also no difference as to the severity of sentencing among the groups. However, with respect to the question “The defendant should be found guilty if there is at least __% chance that he committed the crime.,” the subjects in the relevant videotape group chose a much lower number than other groups. (Ms = 76.56 compared to 93.16 and 92.99)

(d) Douglas, K. S., Lyon, D. R., & Ogloff, J. R. P. (1997). The impact of graphic photographic evidence on mock juror decisions in a murder trial: Probative or prejudicial. Law and human Behavior, 21, 485-501. (Canada)

     Subjects were 120 students (82 female, 38 male) registered in first- and second-year psychology courses. Each subject read 30-page trial transcript of 1st degree murder. Each subject saw photographs of the victim’s apartment building, the door to her apartment, a knife similar to one purchased by the accused sometime before the murder, and a graduation photograph of the victim. All subjects were randomly assigned three groups: [1] Color group, [2] B&W group, and.[3] Control group. Color group saw colored photographs of the stabbed victim’s body, the victim’s face and shoulder. B&W group saw black and white photographs of the same content. Control group did not see any autopsy photographs of the victim. Each subject answered questions without deliberation.

      Subjects in the Color group and the B&W group marked higher conviction rate than subjects in the Control group (Color: 57.5%, B&W: 50%, Control: 27.5%). Difference of groups did not make difference about sentencing decision. Also, there was no difference between groups in terms of whether subjects felt they acted in a fair and unbiased manner in this mock trial.

(e) Bright, D. A., & Goodman-Delahunty, J. (2006). Gruesome evidence and emotion: Anger, blame, and jury decision-making. Law and Human Behavior, 30, 183-202. (Australia)

     Subjects were 102 first-year undergraduate psychology students. Each subject read a 20-page summary of a trial of murder. Each subject was assigned one of the two following conditions: [1] Verbal gruesome evidence or [2] Verbal non-gruesome evidence. Furthermore, each subject was assigned one of the three following conditions: [1] No photographs, [2] Neutral photographs or [3] Gruesome photographs. Each subject answered questions without deliberation.

      With respect to photographs, conviction rates were significantly higher in Neutral photographs group and Gruesome photographs group than in No photographs group. Verbal gruesome evidence did not make difference in No photographs group and Neutral photographs group. Gruesome photographs and verbal gruesome evidence group indicated significantly higher conviction rate than other groups.

(f) Matsuo, K., & Ito, Y., Kanj ōwo Kanki suru Jō333; ga Mogi-saiban-in no Jijitsu-nintei Handan to Negative Kanjōni Oyobosu Eiky #333; (The impact of inflammable information on lay-judges’ fact-finding and negative emotion) (written in Japanese)

      Subjects were 126 undergraduate students (male 37, female 90). Each subject watched and listened to a Powerpoint presentation and narration of the scenario of a murder trial. With respect to graphic gruesome evidence, each subject was assigned no photographs group or gruesome photographs group. Subjects in gruesome photographs group saw a photograph of victim’s autopsy and subjects in no photographs group did not see any photographs of victim’s autopsy. Each subject answered questions without deliberation. Gruesome photographs groups were more likely to convict (73.21%) than no photographs groups (58.93%).

4. Brief Analysis
(1) What Can be Said from These Studies?
      According to these studies, it can be said that gruesome evidence including photographs and video recordings generally has an unfavorable impact for the defendant on jury decision-making. The subjects who saw gruesome photographs were more likely to convict than the subjects who did not see gruesome photographs [(d), (e), (f)]. One study indicated that the subjects did not necessarily notice the impact of gruesome photographs [(d)]. Also, with respect to the question “The defendant should be found guilty if there is at least __% chance that he committed the crime.,” the subjects who saw the videotape of victim’s autopsy chose much lower number than other groups [(c)]. Although in some studies, gruesome evidence did not make difference as to severity of sentencing [(c), (d)], the studies with civil case showed that the subject who saw colored photographs chose higher damage award in some situations [(a), (b)].

(2) Methodological Limitations
There are several methodological limitations many of which come from the difference of real trial and mock jury study.

     A. Subjects are only students
Subjects were undergraduate students. In many cases they were studying psychology. Thus the subjects were younger and more homogeneous, and have less experience in society than real jury. Because of this difference, it is possible that the subjects of these studies made peculiar decision than real jurors.
     B. Difference of seriousness of real jurors and mock jurors
These studies are about mock jurors. In real trial, jurors are more seriously consider the case than mock jurors in these studies.
     C. Non-existence of the Professionals
If professionals including lawyers, prosecutors and judges participated in these studies, the results might have been different and those results might be closer to those in real cases. For example, if lawyers and prosecutors gave opening statements and closing arguments, and judges gave jury instruction and answered questions from the mock jurors, those participations might have affected the seriousness of the mock jurors and brought their better understanding of the cases and legal rules.
     D. Non-existence of jury deliberation
These studies do not include the process of jury deliberation, which is necessary for jury to reach the verdict. If the deliberations were held, the results of these studies might have been different.
     E. Information given to the subjects were less than those in real trials

      In many of these studies, other than seeing gruesome evidence, subjects only read the transcript or summary of the trial, or watched summary presentation. However, in real lawsuit, jurors are given a lot more information throughout the trial. This difference might have overemphasized the impact of gruesome evidence in these studies. In real trial, the impact of gruesome evidence might be reduced, eliminated, or altered in the sea of other information.

(3) Possible Defense Strategies
     Although there are several limitations to these studies, we still think gruesome evidence generally has unfavorable effects for the defendant on jury decision-making. Video recordings or photographs in the Tsarnaev trial also include the gruesome evidence. Therefore, it is useful to think about strategies to avoid/reduce the impact of these evidences.

      The following measures might be useful for the defense lawyer to avoid/reduce the impact of video recordings and photographs.

A. Try to exclude the evidence or limit the use of the evidence on the basis of: irrelevance, prejudice, lack of necessity and so forth.
B. Negotiate with the prosecution not to use gruesome evidence or limit the use of gruesome evidence
C. Call expert witness to inform the court that gruesome evidence could cause prejudicial impact on the jury.
D. Indicate in opening statements and closing arguments that gruesome evidence should not have significant impact. Emphasizing”reasonable doubt” standard of proof would be helpful because one of the studies indicated that the subjects who saw the crime scene videotape chose lower standard of proof.
E. Try to include a warning about gruesome evidence in jury instructions. A specific explanation of “reasonable doubt” standard would also be beneficial.

IV. Conclusion

     Due to the massive collection of video evidence from the bombing site, there is a vast amount of video evidence that places Dhozokar Tsarnaev at the bombing site carrying a black satchel that is presumed to carry one of the bombs that was eventually used in the attack.  Although the amount of video identifying Tsarnaev and placing him at the site is large, there are issues in terms of the presentation of video evidence in the Tsarnaev trial.  Specifically, even though reams worth of videos were collected, the FBI has failed to provide the “smoking gun” evidence that it claimed it had; a video depicting the Tsarnaev brothers placing a black backpack at the scene. In light of the prosecution’s failure to produce evidence, the defense council has motioned to strike all references to this video from the record and from other sources of video evidence.

     As a critical element in the prosecution’s case, the role of video evidence will undoubtedly impact the jury’s decision-making process on an explicit level.  Although Tsarnaev’s guilt is a settled manner, the role of video evidence has the potential to play a crucial role in determining Tsarnaev’s punishment.

i Tom R. Tyler, Viewing CSI and the Threshold of Guilt: Managing Truth and Justice in Reality and Fiction, 115 Yale L.J. 1050, 1050 - 1085 (2006).

ii Id.

iii Id.

iv Id.

v Donald E. Shelton, The ‘CSI Effect’: Does it Really Exist?  259 Natl. Inst. of Just. 1, 1-7 (2008) (finding that viewers of CSI have higher expectations for scientific evidence, but not significant difference in their willingness to acquit as compared to non-CSI viewers)

vi Wendy P.  Heath and Bruce D. Grannemann, How Video Image Size Interacts with Evidence Strength, Defendant Emotion, and the Defendant-Victim Relationship to Alter Perceptions of the Defendant, Behav. Sci. Law 32:496-507 (2014).

vii Vicki L. Fishfader, Gary N. Howells, Roger C. Katz, and Pamela S. Teresi, Evidential and Extralegal Factors in Juror Decisions: Presentation Mode, Retention, and Level of Emotionality, Law and Human Behavior Vol. 20, No. 5 (1996). 

viii Louise Ellison and Vanessa E. Munro, A ‘Special Delivery?  Exploring the Impact of Screens, Live-Links and Video-Recorded Evidence on Mock Juror Deliberation in Rape Trials, Social & Legal Studies Vol. 23(1) 3-29 (2014).

ix Wendy P. Heath, Bruce D. Grannemann and Michelle A. Peacock, How the Defendant’s Emotion Level Affects Mock Jurors’ Decisions When Presentation Mode and Evidence Strength are Varied, Journal of Applied Social Psychology 34, 3 (2004). 

x Neal Feigenson, Visual Evidence, Psychonomic Bulletin & Review 17(2) (2010).

xi Yael Granot et at., Justice is Not Blind: Visual Attention Exaggerates Effects of Group Identification on Legal Punishment. 143(6) J. of Exp’l. Psychol.: Gen. 2196, 2196-2208 (2014).