Last week, Judge Louis Pollack, a former law professor and dean of the Yale Law School, issued what may prove to be a landmark ruling holding that fingerprint "experts" would not be permitted to testify to a definite match between fingerprints found at a crime scene and fingerprints taken from a suspect. Fingerprint evidence, while subject to some criticism over the years by forensic scientists, has generally been the most widely used and cited of all scientific evidence in American courts for the better part of the last century.
Certainly in the public mind, fingerprint evidence has come to be seen as a standard tool of forensic science. Given the fact that there exist vast national databases of fingerprint evidence and that fingerprinting has been suggested as one means to tighten airport security, any serious attack on the validity of fingerprinting must attract attention.
Although Judge Pollack's decision is not applicable outside of a rather narrowly defined jurisdiction, it will have significant influence throughout courts in the United States. There are several reasons for this. First, Judge Pollack is one of the most distinguished judges on the federal bench today and he is known for his knowledge and his good judgment.
Second, the opinion will be viewed in a very special context. Several years ago the Supreme Court of the United States decided a case called Daubert in which it placed the responsibility upon federal judges to decide the admissibility into court of expert "scientific" testimony. The Supreme Court has, since Daubert, continued to insist upon this role for federal judges, one which many federal judges have embraced wholeheartedly.
Given this new power it is not at all surprising that even very traditional forms of scientific evidence, like fingerprint analysis, are coming under increased scrutiny. Given the clarity of Judge Pollack's decision and the positive reputation he enjoys, it seems likely that many other judges also will decide to look again at fingerprint evidence and feel empowered to decide whether it should be used in their courts.
From the practical point of view, the problem with fingerprint evidence in court is that while one can say with a reasonable degree of certainty that no two individuals have the same fingerprints, most fingerprint evidence used in criminal trials involves comparison between prints taken at a crime scene and prints taken from a suspect. It is relatively easy to take clear prints from a suspect in a controlled environment. Crime scene prints are often obscure at best.
It is the forensic expert's role to look at these poor crime-scene prints and determine whether they match those of a particular suspect. This involves subjective judgement on the part of the expert and, as common-sense and Judge Pollack's opinion point out, not all experts are equally trained or equally competent. Judge Pollack decided that there was simply too much uncertainty in the process to deem it sufficiently "scientific" and certain to allow such evidence to be presented in court.
The problem Judge Pollack sees with fingerprint evidence is not unique. Much the same kind of problems arise in a number of examples of "scientific" evidence. Courts increasingly are unwilling to accept the evidence of polygraphs [lie detectors]. Many courts are beginning to question whether ballistic evidence as to whether a particular gun fired a particular bullet can be conclusive or even worthy of presentation in court. The problem, of course, is that science is not a static thing and that even in the most advanced areas of science, there often is a need for human judgment to be used.
In the 19th century, some courts were willing to accept the testimony of phrenologists that bumps on a suspect's head were indicative of criminal inclinations and, therefore, that the suspect was guilty of a particular crime. In Nazi Germany, courts routinely made use of evidence presented by "racial scientists" who testified that members of certain ethnic or religious groups were "subhuman" and criminal and, therefore, a danger to society and guilty of crimes.
Today, many courts are being forced to re-evaluate cases based upon DNA evidence, evidence which the U.S. Supreme Court has said may be presented as evidence [if presented properly]. The fact that so advanced a forensic tool is now available to law enforcement may make Judge Pollack's decision about fingerprint evidence less problematic.
Nevertheless, most police and other law enforcement personnel have come to regard fingerprint evidence as a crucial part of their forensic armory and, if they lose it, will feel that they have lost a major advantage in the battle against crime.
On the other hand, it is a long-honored principle of American jurisprudence that we must err on the side of caution rather than convict innocent people on false evidence. The next few years will determine to what extent fingerprint evidence will survive as a tool for criminal investigation and courtroom use.
Mike Hoeflich is a professor in the Kansas University School of Law.
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