Prosecutors called a string of women to the stand late Wednesday, all of whom were pregnant at the same time as Laci Peterson and walked for exercise in the same area, in an attempt to thwart the defense before it begins its case in early October.
"A lot of this week has been the prosecutors playing defense," said former San Francisco prosecutor and trial observer Jim Hammer. "They're trying to anticipate defense attacks on their case."
Testimony began Thursday with a Stanislaus County district attorney's office investigator talking about fishing spots near the Petersons' home. Scott Peterson claims he was fishing at the Berkeley Marina when his wife disappeared Dec. 24, 2002. The bodies of Laci Peterson and her fetus were later found down the shore from the marina.
Defense lawyer Pat Harris showed Kevin Bertalotto a receipt for a saltwater fishing rod Scott Peterson bought Dec. 20.
"If you want to go saltwater fishing, the Berkeley Marina and bay would be the closest," Harris asked.
"Yeah, probably," Bertalotto answered.
On Wednesday, an FBI DNA expert testified that at least one strand of dark hair found on Peterson's boat probably came from his dead wife.
Prosecutors say the hair found in a pair of pliers is significant because, they contend, Laci was never on the boat and was even unaware her husband had bought one.
Defense lawyers don't concede that the hair belonged to Laci and have offered innocent explanations for how it might have ended up there, including that she was once on the boat and that it may have fallen from Scott Peterson's clothing.
Constance Fisher, an FBI DNA expert who tested the hairs, explained to jurors how the mitochondrial technique used in this case varies from nuclear DNA testing that can produce a virtually definitive genetic fingerprint.
"Mitochondrial DNA cannot be used to point to an individual to the exclusion of all others, as nuclear DNA can be," Fisher said. "It is less discriminating."
The less-precise mitochondrial method is used when the hair tested does not have a root.
Fisher said testing excluded the possibility that the hair came from Scott Peterson and, according to comparisons with a swab taken from Laci's mother's cheek, it likely came from Laci.
She said "about one out of 112" Caucasian people would have the same mitochondrial DNA makeup.
Defense lawyers have attacked the mitochondrial testing, calling it unreliable. They also have attacked the way police collected the hairs.
Detectives testified they took one hair from the pliers. But Detective Allen Brocchini testified that two hairs were discovered when he and another officer opened the evidence envelope months after collecting the single strand.
Only one strand was tested, Fisher said.
Defense lawyer Mark Geragos implied Brocchini may have contaminated the evidence by opening the envelope in a non-sterile environment — a police waiting room.
Karen Korsberg, an FBI trace evidence expert, testified that a visible examination of hairs from one of Laci's brushes indicated it matched the hair from the pliers.
Laci Peterson, eight months pregnant, vanished just before Christmas 2002 from the couple's home in Modesto. Her remains and that of her fetus washed ashore along San Francisco Bay several months later, mere miles from where Scott Peterson claimed he was fishing alone the day she disappeared.
On cross-examination, Korsberg acknowledged she was unaware of a pubic hair collected from duct tape found on Laci Peterson's remains and never compared that to samples she was given from Laci's hairbrush. Fisher, too, said she was unaware of the pubic hair and never tested it for a match to the hairs found in the pliers.
Prosecutors allege Peterson killed his wife in their Modesto home on or around Dec. 24, 2002, then drove to San Francisco Bay and dumped her body from the boat.
Defense lawyers contend someone else abducted and killed Laci while she walked the couple's dog in the neighborhood, then framed their client after learning of his widely publicized fishing alibi.