That is why a landmark April 25 decision from the Pennsylvania Supreme Court upholding experts' use of CGAs is certain to reverberate in courtrooms throughout the United States.
The court held that a CGA is admissible evidence and is to be weighed by the same criteria of admissibility as other evidence – probative value versus prejudicial effect. But the court said that certain concerns prior to admission carry more weight and deserve closer scrutiny for CGAs than for more traditional forms of evidence.
The court also decided that because a CGA is a graphic illustration of an expert's reconstruction rather than a simulation based on computerized calculations, it is not subject to the test governing admissibility of scientific evidence established under Frye v. United States, 293 F. 1013 (D.C. Cir. 1923). Still, the underlying expert opinion that the animation illustrates must satisfy the standards for admissibility of expert testimony.
While Pennsylvania is not the first court to rule on the admissibility of CGAs, it is one of only a few. Coming from the state's highest court, the decision is likely to provide a platform for future courts to decide the issue.
A CGA is a series of computer-created drawings that, when assembled frame-by-frame, produce the image of motion. "The image is merely a graphic representation depicting the previously formed opinion of a witness or witnesses," the court's opinion said.
It is distinct from a computer-generated simulation, which uses software to analyze data and reach a conclusion, the court noted. "A CGA is only as credible as the underlying testimony that it represents and the computer plays no part in calculating an outcome or presenting its own conclusions."
The CGA in issue was used in the first-degree murder trial of Michael Serge, who was found guilty of killing his wife. Before trial, the prosecution sought permission to use the CGA to illustrate the opinions of two experts, a forensic pathologist and a crime scene reconstructionist.
The trial judge ruled that he would allow the CGA, provided the prosecution authenticated it as a fair and accurate depiction of the expert reconstructive testimony, excluded any inflammatory features that could cause unfair prejudice, and provided it to the defense before trial.
At trial, the court twice instructed the jury about the purely demonstrative nature of the CGA, once before it was presented and again during the jury charge prior to deliberation. The judge told the jury that the CGA was a demonstrative exhibit, not substantive evidence, and that it was being offered solely as an illustration of the prosecution's version of the events.
"The court informed the jury that they should not confuse art with reality and should not view the CGA as a definitive recreation of the actual incident," the Supreme Court recounted.
After the defendant was found guilty of first-degree murder, he appealed. The Supreme Court took the case solely on the issue of the admissibility of the CGA, a question it had never decided.
In beginning her analysis for the Supreme Court, Justice Sandra Schultz Newman noted that judges must "shed any technophobia and become more willing to embrace the advances that have the ability to enhance the efficacy of the legal system." But she quickly added that even though CGAs represent new technology, the rules for analyzing their admission are the same as those that govern traditional forms of demonstrative evidence.
It analogized these experts' use of CGAs to chalk diagrams or sketches on a blackboard. "The difference is one of mode, not meaning. The law does not, and should not, prohibit proficient professional employment of new technology in the courtroom. This is, after all, the twenty-first century."
Applying these traditional rules, the court said that the CGA satisfied the requirements of its three-pronged test for admissibility – it was properly authenticated, was relevant, and its probative value was not outweighed by the danger of unfair prejudice.
But the court added a new factor for judges to consider when evaluating a CGA: the dangers and benefits this type of demonstrative evidence presents as compared with more traditional forms. Given this, the Supreme Court said, a trial court should issue limiting instructions to the jury explaining the nature of the specific CGA.
With respect to authentication, the court said that the prosecution properly laid the foundation showing that the CGA was what it purported to be, "a depiction of the various testimonies of the Commonwealth witnesses concerning their theory about the chain of events."
As to the CGA's relevance, the court found that it was. "[I]t clearly, concisely, and accurately depicted the Commonwealth’s theory of the case and aided the jury in the comprehension of the collective testimonies of the witnesses without use of extraneous graphics or information."
The court then turned to the question of prejudice, where the court said the CGA had the greatest potential danger because of its visual nature. But the court found that the CGA used in this case "was neither inflammatory nor unfairly prejudicial." Any prejudice in the visual depiction was not the fault of the CGA, the court said, "but rather was inherent to the reprehensible act of murder."
If there is danger in using a CGA, it can be mitigated through cautionary jury instructions, the court said. "Although limiting instructions may not be necessary, such cautionary instructions limit the prejudice or confusion that could surround a CGA."
Noting that the trial judge cautioned the jury twice – once when the CGA was shown and again in his jury charge – the court said he "duly minimized any possible prejudice by insisting that the jury not make more of the CGA than what it was – an illustration of expert witness testimony."
Based on this analysis, the court affirmed the trial court's decision to allow the CGA.
The case is Commonwealth v. Serge, Case No. J-37-2005 (April 25, 2006).