Juries are awed by forensic science in the courtroom. Fingerprint comparison, DNA, handwriting analysis, ballistics, blood-splatter, shoe print comparison, etc. Prosecutors across the county depend upon this evidence to obtain convictions and juries are conditioned by television shows, like CSI, to expect it. However, a recent report from the National Academy of Sciences says much of what passes for forensic "science" does not meet minimal scientific standards. Yet, when forensic scientists testify in court they are often shamefully overconfident about their "scientific" findings.
Following are several significant problems identified by the study:
1. Bias: Forensic scientists are often exposed to information which fosters bias in their stated opinions. That is, forensic "scientific" tests are rarely performed "blind." The examiner knows what they are supposed to find in the samples, which effect the outcome of their testing. Contrast this with doctors who test a new medicine. They are not told which patients are taking the medication and which ones are receiving placebos. This is appropriate "blind" testing and eliminates bias.
2. Error Rates: Most forensic sciences lack good information about how often examiners make mistakes - a basic requirement of any good science. Experts testifying in court often claim error rates for their technique is zero. Preposterous! Even the best of scientific techniques have an error rate. Without objective information about a technique's rate of error a jury cannot properly assess the credibility of the information.
3. Over-claiming: The only forensic science making regular use of probabilities is DNA profiling in which experts testify to the probability of a match. None of the traditional forensic sciences (ballistics, fingerprints, fiber analysis, or handwriting) currently have the necessary statistical foundation to establish accurate probabilities. Adding insult in injury, experts who testify are allowed to claim their methods are 100% accurate. Again, preposterous.
4. Structural Independence: The cops and prosecutors employ and pay the experts who testify in court. Do you believe these experts might have difficulty maintaining their professional independence from police and prosecutors who put food on their tables? I dare to say, yes.
So what can be done to control this "out-of-control" system leading to the condemnation of thousands of accused persons each year?
First, judges presiding over trials in which forensic evidence is used must exercise their role as gatekeepers to protect the integrity of our criminal justice system. They do this by requiring higher standards for forensic science when used as legal evidence. They should prohibit experts from testifying to impossibilities like "zero" error rates. They should compel the experts to establish the reliability of their scientific techniques with peer review and other methods establishing the credibility of their testimony.
Second, the criminal defense lawyers who defend the accused must object to the use of forensic evidence until the proponent proves its scientific reliability. That means the defense lawyers must learn about the forensic methods being used, learn about the scientific pitfalls, and raise objections in court based on established case law requiring judges to make findings of reliability. Finally, they must hire their own defense experts to dispute the prosecutor's evidence and cast doubt upon its credibility.
Our justice system demands no less.