Are crime dramas warping the legal system? The CSI effect

Television dramas that rely on forensic science to solve crimes are affecting the administration of justice.

In 2008 Monica Robbers, an American criminologist, defined the CSI effect as “the phenomenon in which jurors hold unrealistic expectations of forensic evidence and investigation techniques, and have an increased interest in the discipline of forensic science.”

Now another American researcher has demonstrated that the “CSI effect” is indeed real. Evan Durnal of the University of Central Missouri’s Criminal Justice Department has collected evidence from a number of studies to show that exposure to television drama series that focus on forensic science has altered the American legal system in complex and far-reaching ways. His conclusions have just been published in Forensic Science International.

The most obvious symptom of the CSI effect is that jurors think they have a thorough understanding of science they have seen presented on television, when they do not. Mr Durnal cites one case of jurors in a murder trial who, having noticed that a bloody coat introduced as evidence had not been tested for DNA, brought this fact to the judge’s attention. Since the defendant had admitted being present at the murder scene, such tests would have thrown no light on the identity of the true culprit. The judge observed that, thanks to television, jurors knew what DNA tests could do, but not when it was appropriate to use them.

According to Mr Durnal, prosecutors in the United States are now spending much more time explaining to juries why certain kinds of evidence are not relevant. Prosecutors have even introduced a new kind of witness—a “negative evidence” witness—to explain that investigators often fail to find evidence at a crime scene.

Defence lawyers, too, are finding that their lives have become more complicated. On the positive side, they can benefit from jurors’ misguided notion that science solves crimes, and hence that the absence of crime-solving scientific evidence constitutes a reasonable doubt and grounds for acquittal. On the other hand they also find themselves at pains to explain that one of television’s fictional devices—an unequivocal match between a trace of a substance found at a crime scene and an exemplar stored in a database, whether it be fingerprints, DNA or some other kind of evidence—is indeed generally just fiction.

In reality, scientists do not deal in certainty but in probabilities, and the way they calculate these probabilities is complex. For example, when testifying in court, a fingerprint expert may say that there is a 90% chance of obtaining a match if the defendant left the mark, and a one in several billion chance of a match if someone else left it. In general DNA provides information of a higher quality or “individualising potential” than other kinds of evidence, so that experts may be more confident of linking it to a specific individual. But DNA experts still deal in probabilities and not certainties. As a result of all this reality checking, trials are getting longer and more cases that might previously have resulted in quick convictions are now ending in acquittals.

The CSI effect can also be positive, however. In one case in Virginia jurors asked the judge if a cigarette butt had been tested for possible DNA matches to the defendant in a murder trial. It had, but the defence lawyers had failed to introduce the DNA test results as evidence. When they did, those results exonerated the defendant, who was acquitted.

Continue Reading in the Economist.

H/T Mindhacks