The fight over a hair found in Scott Peterson's boat continued Monday, with a defense expert criticizing the DNA techniques used 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 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 the boat may back up 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 spot in San Francisco Bay where he dumped it.
The couple's relatives 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.
There is no evidence that Laci Peterson was ever in the boat, raising the question of how the 6-inch strand of hair, which could be hers, got there.
The remains of the 27-year-old substitute teacher and her unborn son 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.
Shields said the FBI had also used a faulty statistical method that skewed the probability that the hair could have come from anyone other than Laci Peterson. The FBI expert said the DNA extracted from the hair is found in one in 112 white people. Shields said it is found in about one in 10 white people.