by Debra Mares
Most people become lawyers because they’re neither mathematicians nor scientists. Yet many criminal cases involve forensic science, which is widely accepted by juries and serves as the basis of many crime television shows. A forensic pathologist can tell us the cause of death. A gas chromatograph can tell us a driver’s blood alcohol level. DNA can tell us the identity of a sexual assault perpetrator. A polygraph can tell us whether a suspect is telling the truth. A plethysmograph can tell us an offender’s sexual preference. Physics can tell us how a collision occurred. Today, scientific evidence is often admitted in court without legal argument; however, it took a long journey for it to become so widely accepted.
In Frye v. United States (D.C. Cir. 1923) 293 F. 1013, the court addressed the admissibility of polygraph evidence in court. Frye resulted in a holding that set forth the standard for determining the admissibility of all scientific evidence. The Frye standard required the science involved to be generally accepted in the relevant scientific community. (Id. at p. 1014).
In 1993, the United States Supreme Court replaced the Frye standard with the Daubert standard. In Daubert v. Merrell Dow Pharmaceuticals (1993) 509 U.S. 579, the court outlined the factors determining admissibility of expert scientific testimony, which included: (1) whether the theory or technique on which the testimony is based is capable of being tested; (2) whether the theory or technique has a known rate of error in its application; (3) whether the theory or technique has been subjected to peer review and publication; (4) the level of acceptance in the relevant scientific community of the theory or technique; and (5) the extent to which there are standards to determine the acceptable use of the theory or technique. (Id. at pp. 591-594).
Using these factors, state and federal courts throughout the country began to reexamine bans on polygraph tests. In California, Evidence Code section 351.1, subdivision (a) excludes the results of polygraph examinations in criminal cases, unless all parties stipulate to admit them. Although polygraph results are inadmissible, Evidence Code section 351.1, subdivision (b) allows the admission of statements made during a polygraph, provided they meet a hearsay exception. In practice, the interviewee often makes statements about the crime during a “post-interview,” which may be helpful to the prosecution and otherwise admissible as a party admission under Evidence Code section 1220 or a declaration against interest under Evidence Code section 1230.
As legally accepted as science is in the courtroom, it still has its practical limits, as any effective trial counsel appreciates. For example, it is critical to select jurors for a trial who are not biased regarding the use of science in a criminal case. Some people simply don’t trust modern-day science and consider it “junk.” It is important to help jurors understand that scientific evidence is not gathered and analyzed as quickly or easily as it appears in their favorite television show. Limited budgetary resources often hinder widespread use of scientific analysis in cases.
Crime shows set the bar high when it comes to what juries expect real-life forensic examiners to do and how fast they expect them to do it. Crime laboratories work on a case-by-case basis and must comply with strict regulations and guidelines to maintain their licensing credentials. New cases come into the laboratory and compete for attention with old cases, which are oftentimes cold, having been sitting in evidence vaults for years waiting for analysis. DNA results in the real world are not revealed within the timeframe of a 60-minute television episode. Rather, they may take days, weeks or months, depending on the availability of resources and experts.
Remaining humble about scientific results will help achieve just results in our criminal justice system. Science does not always tell us the motive or intent of a perpetrator. If a suspect’s bodily fluid is found inside a victim’s sexual organs, it doesn’t tell us whether there was consent. Even if a suspect’s fingerprint is found inside a store recently robbed, it doesn’t necessarily tell us when he was there.
Despite its limits, one of the greatest uses of science is to vindicate a suspect. Polygraph tests are often used early on in investigations or at the suggestion of defense attorneys who believe that passing results will raise doubt in a prosecutor’s mind or motivate discussion of a plea bargain. DNA testing can often be used to rule out a suspected perpetrator. Any effective trial counsel will never under or overestimate the value of science, nor lose sight of the importance of old-fashioned police work and eyewitness testimony to corroborate strong scientific findings.