U.S. Supreme Court (Rulings on Forensic Evidence)
Throughout the twentieth century, the court system wrestled with the issue of whether the testimony of forensic experts was a valid form of evidence. The essential problem was that modern science moves at a brisker pace than the judicial system. As new scientific techniques with applicability to forensics emerged, the courts often had no precedents on which to accept or reject them. Today, for example, the validity of fingerprint identification, with its axiom that the fingerprints of no two persons are alike, is largely taken for granted. But a century ago the courts were not so sure, for there was little research to buttress such a claim. At the opposite end of the twentieth century came DNA evidence, with statistical claims about the uniqueness of a person's genetic markers left behind at crime scenes in the form of blood, semen, skin cells, or hair. While justice plods, science sprints, often leaving the court system struggling to catch up as it tries to answer fundamental questions about the validity of scientific testimony and how to distinguish the claims of science from those of pseudoscience.
The United States Supreme Court has decided very few cases that directly bear on the admissibility of forensic testimony. Rather than addressing the issue of the validity of any particular branch of forensic science, the Court has limited itself to establishing ground rules for forensic testimony. Currently, it does so through the Federal Rules of Evidence, a set of broad principles used in federal trials. Most state courts have adopted these rules as well. The Federal Rules govern a number of issues pertaining to the relevance of evidence, but the key rule for forensic scientists is Rule 702, "Testimony by Experts," which applies to the testimony of any forensic scientist called to the witness stand: "If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise, if (1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case."
The Court entered the arena of forensic science in a 1923 case, Frye v. United States. Frye had been convicted of second-degree murder. His lawyer wanted to offer the testimony of a scientist who had conducted a systolic blood pressure deception test, today called a lie-detector or polygraph test, to demonstrate that his client was telling the truth. The trial court refused to admit the testimony, and the defendant appealed. In a remarkably brief and pointed decision, the Supreme Court affirmed the ruling of the lower court, famously stating: "Just when a scientific principle or discovery crosses the line between the experimental and demonstrable states is difficult to define. Somewhere in this twilight zone the evidential force of the principle must be recognized, and while courts will go a long way in admitting expert testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs." In the Court's view, the systolic blood pressure deception test had "not yet gained such standing and scientific recognition."
Thus was born the so-called Frye standard, used in the years that followed by various lower courts to rule on the admissibility of such forensic tools as voiceprints, neutron activation, gunshot residue tests, bite mark comparisons, and blood grouping tests. The fundamental principle was "general acceptance in the particular field," making the scientific
community itself the arbiter of whether a technique or procedure passed scientific muster. In a key case affirming the Frye standard in 1974, a U.S. Court of Appeals wrote in United States v. Addison that the standard "assures that those most qualified to assess the general validity of a scientific method will have the determinative voice." Thus, the Frye standard remained a well-settled principle for 70 years.
By the 1990s, though, the Frye standard was coming under pressure, largely because in 1975 the Federal Rules of Evidence were enacted, and nowhere did they mention the "general acceptance" test of Frye. The rules seemingly cleared the way for admitting scientific testimony based on new knowledge that had not necessarily gained general acceptance in the scientific community. Uncertainty over the question of whether the Federal Rules superceded the Frye standard had come to a head in 1993 when the Supreme Court heard the case of Daubert v. Merrell Dow Pharmaceuticals.
The case involved two children with serious birth defects. Daubert contended that the defects were caused by a Merrell Dow drug the mother had taken during pregnancy. He wanted to offer the scientific testimony of eight experts who had conducted animal studies and chemical structure analyses on the drug and concluded that it could cause birth defects. The company responded with published scientific epidemiological studies showing that the drug was not a risk factor for birth defects. The trial court, citing Frye, agreed with the company and ruled that the methods employed by the plaintiff's experts did not meet the standard of "general acceptance" under Frye. The Court of Appeals affirmed the trial court's ruling, but the U.S. Supreme Court reversed the Court of Appeals.
In its opinion, the Court undertook a detailed examination of whether the Federal Rules of Evidence superceded Frye. It concluded that Frye's 'general acceptance' is not a necessary precondition to the admissibility of scientific evidence" and that the Federal Rules "assign to the trial judge the task of ensuring that an expert's testimony both rests on a reliable foundation and is relevant to the task at hand." To guide the trial judge, the Court offered a flexible four-pronged test based on whether the theory or technique has been "tested"; whether it has been subjected to "peer review," usually through a peer-reviewed publication, so that the scientific community can detect flaws; what its "known or potential rate of error" is; and its "acceptability" in the relevant scientific community. Accordingly, the more stringent Daubert (pronounced "Dough-BEAR") standard replaced the earlier Frye standard. Judges, not the scientific community, were to determine reliability and relevance.
The Daubert standard came into play in a 1997 case, General Electric Co. et al. v. Joiner. After he was diagnosed with lung cancer, Joiner sued General Electric and Monsanto. He proffered expert testimony that the cancer was caused by his exposure to workplace chemicals the companies manufactured. The trial court ruled in favor of the companies' motion to exclude the testimony, saying that the testimony did not rise above "subjective belief or unsupported speculation." The Court of Appeals reversed the trial court, but the Supreme Court concluded that the trial court had acted appropriately under Daubert and that in failing to defer to the trial court's judgment that there was "too great an analytical gap between the data and the opinion" in the animal studies on which Joiner's expert testimony was based; the Court of Appeals had overstepped its boundaries. In other words, the trial court judge had exercised his proper role under the Daubert standard by acting as a "gatekeeper" for expert scientific testimony.
It remained for the Court to determine whether the Daubert standard applied just to "scientific" testimony or to any other type of technical, skill-based, or experience-based knowledge on which expert testimony is based. It did so in Kumho Tire Co., Ltd., et al. v. Carmichael et al. in 1999. Carmichael was driving a vehicle on which a tire blew out. When the vehicle overturned, one passenger died and others were injured. Carmichael sued the tire manufacturer, offering the testimony of a tire failure analyst who concluded that the tire blew out because of a manufacturing defect. Kumho moved to have the testimony excluded on the grounds that the expert's methodology failed to satisfy the requirements of Rule 702 of the Federal Rules of Evidence. The trial court granted the motion, ruling that the expert's testimony failed the four-pronged test outlined in Daubert. In reversing the trial court, the Court of Appeals ruled that the Daubert standard applied only to scientific testimony. While the Supreme Court reversed the Court of Appeals, agreeing with the trial court that the tire expert's procedures failed the Daubert standard, the Court explicitly stated that "The Daubert factors may apply to the testimony of engineers and other experts who are not scientists" and that "The Daubert 'gatekeeping' obligation applies not only to 'scientific' testimony, but to all expert testimony. Rule 702 does not distinguish between 'scientific' knowledge and 'technical' or 'other specialized' knowledge, but makes clear that any such knowledge might become the subject of expert testimony."
Since 1993, the Daubert standard, as fortified by Kumho Tire, has raised the question of whether any form of widely accepted forensic testimony can be challenged. In January 2002, for example, influential Philadelphia judge Louis H. Pollock caused consternation in the law enforcement community when he ruled that fingerprint analysis failed the Daubert standard, though in March 2002, he reversed himself. The likelihood remains that further Daubert challenges to forensic science will be mounted.
