| Peterson expert questions DNA technique used by prosecutors Monday - November 3, 2003 The big fight over a little hair found in Scott Peterson's boat continued Monday with a defense expert criticizing the DNA techniques used by the FBI to link Laci Peterson to the boat her husband said he took fishing the day she vanished. William Shields, a biology professor from the State University of New York at Syracuse, testified that undetected mutations of mitochondrial DNA could skew results and he said the FBI used a sample size that was too small to detect contamination of the hair. The 14-foot aluminum Gamefisher boat is central to both the prosecution and the defense. While providing Peterson's alibi that he was fishing when his wife disappeared from their Modesto home on Christmas Eve, a possible prosecution argument is that he used the boat to ferry her body to a watery grave in San Francisco Bay. Family members of the couple said they didn't know Scott Peterson had purchased the boat,and Laci Peterson's mother said her daughter generally told her about expensive purchases they made such as sofas, a barbecue grill and a swimming pool. There is no evidence so far that Laci Peterson was ever in the boat, raising the question of how the 6-inch strand, which could be hers, ended up in the boat. The remains of the 27-year-old substitute teacher and the baby boy she was carrying washed ashore in April about three miles from where Scott Peterson said he was fishing. Defense lawyer Mark Geragos has attacked the DNA testing used to compare the hair with the genes of Laci Peterson's mother, Sharon Rocha, as unreliable and fraught with errors. He also claims the sample may have been tainted with other genetic evidence and was possibly tampered with by police. While the sample was originally recorded in evidence files as a single hair, Geragos said the envelope later contained two strands.Prosecutors said the hair broke in half. Shields, who wore a necktie of the double helix DNA model, said the FBI had also used a faulty statistical method that skewed the probability that the hair could have come from anyone else other than Laci Peterson. The FBI expert said the DNA extracted from the hair is found in 1 in 112 whites, but Shields said that was off by a factor of 10. He said it would be found in about 1 in 10 whites. Genetics lessons have dominated the four-day hearing in Stanislaus County Superior Court to determine if Peterson, 31, stands trial for murder in the deaths of his wife and unborn son. Prosecutors are seeking the death penalty. Mitochondrial DNA has rarely been admitted in California courts and the prosecution must clear three hurdles to use the evidence. They must show the technique is accepted by forensic scientists, that the witness is a bona fide expert and that the testing and analysis was done properly. Shields refused to say whether the technique was generally accepted in the scientific community, saying that was a decision the judge must make. The use of mitochondrial DNA in criminal cases is limited and cannot specifically identify an individual. If matched with similar samples from a family member, it can show a statistical likelihood of identification. On cross examination, Shields said he expected to be paid $4,000 for his work in the case and said he gets as much as 60 percent of his income from testifying for the defense in criminal cases. He rarely works for prosecutors. He also said he had never extracted mitochondrial DNA for forensic purposes and is not a forensic scientist. The hearing resumes Tuesday with defense lawyer Kirk McAllister cross-examining a police witness who testified last week. The proceedings are expected to be brief because Geragos has to return to Los Angeles for a murder trial in which the jury is deadlocked. Scott Peterson said he was willing to waive his right to keep the preliminary hearing moving forward so his lawyer could handle the other case. "Yes, that's fine your honor," Peterson said. PRELIMINARY HEARING INDEX COURT DATES HOME INDEX LACI SCOTT EVIDENCE-NEWS TRIAL VERDICT WITNESS LIST WIRETAPS AMBER |
| LACI & CONNER Forever In Our Hearts |
| PRELIMINARY HEARING DAY 4 William Shields Takes The Stand |
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