Witness, Geragos spar over DNA
Members of the Ceres High School criminal justice class got in line at 5 a.m. Thursday so they could get into Courtroom 2 to sit in on the hearing. From right are Brianne Cooney, Marissa Andreasen, Shawna Eavis and Stacy Schuber. BART AH YOU/THE BEE
Peterson defense attorney Mark Geragos grilled Constance L. Fisher, a DNA expert for the FBI, about testing techniques. LAURIE McADAM/THE BEE
Scott Peterson consulted notes during a portion of Thursday's DNA testimony at his preliminary hearing. LAURIE McADAM/THE BEE
Joe and Janey Peterson -- Scott Peterson's brother and sister-in-law -- leave the Stanislaus County Courthouse after Thursday's testimony. AL GOLUB/THE BEE
By JOHN COTÉ
and GARTH STAPLEY
Last Updated: October 31, 2003, 05:37:06 AM PST
A federal DNA expert concluded her testimony Thursday after a second grueling day on the stand as Scott Peterson's defense sought to show a disputed DNA technique is unreliable and should be excluded from court.
Stanislaus County Superior Court Judge Al Girolami is set to hear testimony Monday from a defense DNA expert before making a decision on the issue.
FBI expert Constance L. Fisher was the only witness to testify for the second straight day in Peterson's preliminary hearing on double-murder charges.
FBI lab technicians used mitochondrial DNA testing on a single hair found attached to pliers in Peterson's boat and determined 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 evidence linking Laci Peterson to the boat that her husband said he took fishing to San Francisco Bay on Dec. 24, the day she was reported missing. He said she was missing 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 the bay's eastern shore, several miles from where her husband said he went fishing.
Defense attorney Mark Geragos spent much of Thursday questioning Fisher in an attempt to show that mitochon- drial DNA was a scientifically disputed technique. Geragos also tried to show that faulty equipment colored the FBI's results.
Fisher, who rolled her eyes at a question just 16 minutes into the morning session, held her ground under repeated questioning, saying the technique is widely regarded as accurate and scientifically valid.
"There is always debate going on in a community," Fisher said. But, she said, disputes about mitochondrial DNA are not "sizable."
Fisher acknowledged the FBI lab equipment could be "persnickety," but said routine problems did not compromise test results.
Mitochondrial DNA differs from nuclear DNA, which is found in the nucleus of a cell and positively identifies tissues. Mitochondrial DNA is found elsewhere in a cell and cannot be used as a unique identifier.
A maternal tie
Mitochondrial DNA is passed down from one's mother, and all maternal family members share the same mitochondrial DNA in most cases, Fisher said.
Mitochondrial DNA analysis can rule out a match with a known sample, but cannot show that a test sample came from a specific person.
Fisher testified that the hair found in Peterson's boat could have come from Laci Peterson's mother or brother. Laci Peterson's half sister, Amy Rocha, has a different mother.
Geragos attempted to show that the FBI failed to follow its own guidelines, asking Fisher why the FBI lab did not extract DNA from one of Peterson's bones and compare it with the hair.
Fisher said that was not necessary because analysts had a viable saliva sample from Peterson's mother, Sharon Rocha, and that analyzing DNA from a bone is more difficult than from a saliva sample.
FBI guidelines Geragos read in court said technicians "should" compare results with a second tissue sample.
"'Should' has wiggle room in it," Fisher said. "There is a difference between 'should' and 'must.'"
Geragos also took aim at the computer
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