A majority of states profess adherence to the Frye rule, although a growing number have adopted variations on the helpfulness standard suggested by the Federal Rules of Evidence.įrye predicates the admissibility of novel scientific evidence on its general acceptance in a particular scientific field: "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."2 Thus, admissibility depends on the quality of the science underlying the evidence, as determined by scientists themselves. United States has been the most frequently invoked one in American case law. The test for the admissibility of novel scientific evidence enunciated in Frye v. A host of subsidiary questions with respect to how expert evidence should be handled before and during a trial to ensure prompt and effective adjudication apply to all evidence and all experts and are not dealt with in this chapter. The advent of DNA typing technology raises two key issues for judges: determining admissibility and explaining to jurors the appropriate standards for weighing evidence. As in criminal cases, laboratories and other interested parties must treat evidence according to established protocols. In a civil case, however, if the results of a DNA analysis are not conclusive, it will usually be possible to obtain new samples for study. The relevant federal rules (403, 702-706) and most state rules of evidence do not distinguish between civil and criminal cases in determining the admissibility of scientific data. In civil (noncriminal) cases-such as paternity, custody, and proof-of-death cases-the standards for admissibility must also be high, because DNA evidence might be dispositive. The laboratories used for analysis must be reliable and should be willing to meet recognized standards of disclosure. All materials relied on by prosecution experts must be available to defense experts, and vice versa. Wherever possible, a preserved sample should be large enough to enable the defense to obtain an independent RFLP analysis, but there should almost always be enough at least for PCR analysis, a technique likely to be widely used in forensics in the near future for amplification of the DNA in the evidentiary sample. The Fourth Amendment provides much of the legal framework for the gathering of DNA samples from suspects or private places, and court orders are sometimes needed in this connection. As in any forensic work, they must attend to the essentials of preserving specimens, labeling, and the chain of custody and to any constitutional or statutory requirements that regulate the collection and handling of samples. They should take care to minimize the risk of contamination and ensure that possible sources of DNA are well preserved and properly identified. To produce biological evidence that is admissible in court in criminal cases, forensic investigators must be well trained in the collection and handling of biological samples for DNA analysis. Finally, we make a series of practical recommendations, with judges especially in mind. Discussion of case law is intended mainly to highlight specific issues and is not intended to be comprehensive. In that context, we review some of the rapidly growing number of cases involving admissibility. We begin with a discussion of the investigation stage, but devote most of our attention to admissibility. The DNA typing discussed in this chapter is mainly standard single-locus RFLP typing on Southern blots without apparent band shifting i.e., it is the technique most often considered by the courts to date. This chapter provides an overview of how DNA evidence might be used in the investigation and prosecution of crimes and in civil litigation.
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