When the bound body of Nora Sole was found on February 8, 1992, the police in New Plymouth, New Zealand, had few clues. Who would rape and suffocate to death an 83-year-old widow? However, long hairs were found that had not come from the victim, and the semen recovered from the body and stained bedding almost certainly belonged to the rapist. From the semen samples, forensic scientist Debbie Monahan was able to recover DNA and identify patterns from five of its regions, or loci. Even though these five regions accounted for a mere 0.001 percent of the total human DNA, Monahan could estimate that the DNA from only 1 person in 260 million would be expected to match this particular pattern. The New Plymouth police then requested blood samples from area men with long hair, and Monahan determined the DNA profiles for each. After 450 men had been excluded, the police distributed a flyer asking for information about any long-haired man who might recently have had his hair cut. In this way they were led to Gary Ladbrook, whose blood did give a DNA profile that matched that from the crime scene. Confronted with this evidence, Ladbrook pled guilty to rape and murder, adding to the growing list of convictions worldwide that have been obtained with the help of DNA evidence.
DNA was first used in a criminal investigation in 1985, when Professor Alec Jeffreys at Leicester University in England applied his newly developed means of identifying DNA regions first to exonerate a suspect in a double homicide and then to identify the guilty man. By the end of July 1992, DNA samples had been examined in nearly 11,000 cases and admitted into 750 trials in the United States alone. Why, then, has the use of this tool been opposed by some geneticists?
As with any laboratory procedure, it is always prudent to question the adequacy of personnel training, the appropriateness of the protocols, the attention paid to custody of the samples, and the safeguards against gross errors (such as mislabeling blood samples). All such issues have been raised in court and have been answered by descriptions of the great care being taken by forensic laboratories. The forensic science profession was hurt by allegations of less than adequate attention to experimental protocol in People vs. Castro in New York in 1989, when, for the first time, DNA evidence was kept from being used in a court of law. Even in that case, however, a match between the victim's blood and that found on the watch of the defendant was determined correctly. Today, it is rare for any challenges to the laboratory work to be successful.
Instead, successful court challenges have been made to the kinds of calculations that allowed Monahan to cite the number 260 million. As the result of one such
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