2nd FBI expert to defend tests based on DNA
By JOHN COTÉ
BEE STAFF WRITER
Last Updated: November 12, 2003, 05:58:45 AM PST
Testimony over a disputed DNA technique is expected to again dominate Scott Peterson's preliminary hearing on double-murder charges, with a second FBI expert set to testify today.
Prosecutors have indicated that they will call Bruce Budowle, described as one of the "principal architects" of the FBI's DNA typing program, in a bid to counter defense arguments that the DNA test used by the FBI in the Peterson case is unreliable and should be excluded from court.
The preliminary hearing is scheduled to resume at 9:30 a.m. in Stanislaus County Superior Court in Modesto after a five-day break.
Of the six days of testimony so far, three have been devoted to technical and exhaustive questioning of experts about mitochondrial DNA.
FBI lab technicians used mitochondrial DNA testing on a single hair found attached to pliers in Peterson's boat and determined that it could not have been his, but may have been his wife's.
If the FBI findings hold up, the hair could be a key piece of physical evidence linking Laci Peterson to the boat that her husband said he took fishing to San Francisco Bay on Dec. 24, the day that she was reported missing.
Peterson told police that his wife was gone when he arrived back at their Modesto home.
Laci Peterson, 27, was almost eight months pregnant at the time. Scott Peterson, 31, is charged with murdering his wife and their unborn son, Conner. Prosecutors are seeking the death penalty.
Laci Peterson's body and that of her son were found in April along San Francisco Bay's eastern shore, several miles from where Peterson said he went fishing.
A defense expert last week blasted the DNA technique, saying it can produce false results and relies on a flawed database for analysis. The process also is susceptible to contamination, said William Shields, a professor of biology at the State University of New York, Syracuse.
Shields testified that FBI techniques do not take into account evolving genetic science and could wrongly rule out a DNA sample coming from a given individual.
Unlike more commonly known nuclear DNA, mitochondrial DNA analysis can rule out a match with a known sample, but cannot show that a test sample came from a specific person.
Mitochondrial DNA is passed down from women to their children, and all maternal family members share the same mitochondrial DNA in most cases.
Under California law, evidence from a novel scientific technique cannot be admitted in court unless a judge determines it is generally accepted by the relevant scientific community.
FBI expert Constance L. Fisher testified earlier that the technique was widely accepted and considered valid.
The defense is trying to show that the method is in dispute.
Peterson's case is the first California case in which mitochondrial DNA is being offered for forensic evidence. It has been admitted as evidence apparently for another purpose in a San Diego court.
Well, maybe it wasn't offered for forensic evidence, but mitochordrial DNA was done in the Westerfield case.
Catherine Theisen, who examines mitochondrial DNA at the FBI crime lab, said she and an assistant studied four hairs that the San Diego Police Department sent on Feb. 14.
A hair found on a bathmat in the motorhome "cannot be excluded from coming from Danielle van Dam," Theisen said.
Mitochondrial DNA, Theisen explained, is carried down from the mother's side and is primarily used to study hair, bones and teeth.
DNA Expert link Westerfield To Danielle