Investigators handling the double-murder case against Scott Peterson used an increasingly rare and legally risky tactic by interviewing a witness using "hypnosis techniques," legal observers said Tuesday.
"They're taking a risk," said Dr. David Spiegel, associate chairman of psychiatry at Stanford University. "There must be some reason why they want to take that risk."
The jeopardy stems from a state law passed in 1984 that severely restricts the use of information from a hypnotized witness at trial -- including limiting the testimony to matters the person recalled before the hypnosis.
The law was in response to a 1982 California Supreme Court ruling saying that "most experts agree that hypnotic evidence is unreliable because a person under hypnosis can manufacture or invent false statements."
Since the 1984 law, hypnotism largely has been shelved in criminal investigations, but it's sometimes used when police run out of leads, observers said.
"If you hit a dead end, you might come up with some facts that would help you," said Roger C. Park, an evidence law specialist at the University of California's Hastings College of the Law in San Francisco.
An example would be a kidnap victim who under hypnosis remembers details such as riding in a car driven on a gravel road and then over a bridge, Park said.
"You go there and find some evidence, and then you don't need that testimony," Park said. "That's what you're hoping during the investigation."
But prosecutors handling Peterson's case indicated in court last week that they intend to introduce testimony from a Modesto woman who appears to have been hypnotized.
Kristen Dempewolf, who lives in Peterson's La Loma neighborhood, was questioned in a "cognitive interview where hypnosis techniques were used," according to documents prosecutors filed in Stanislaus County Superior Court.
Dempewolf was questioned as police probed the disappearance and death of Peterson's pregnant wife, Laci.
Dempewolf, 33, owns a dog and was in roughly the same stage of pregnancy as Laci Peterson when Peterson was reported missing Christmas Eve.
Two witnesses have said they saw Laci Peterson walking her dog after 9:30 a.m. Dec. 24 -- the time her husband told police he left for a solo fishing trip.
Scott Peterson told police Laci was preparing to walk the couple's golden retriever, McKenzie, when he left for San Francisco Bay, and he returned from the trip to find his wife missing.
Prosecutors contend that he killed his wife and unborn son, Conner, on Dec. 23 or Dec. 24. Their bodies were found in April along the eastern shore of the bay, within four miles of where Scott Peterson said he launched his boat Christmas Eve. The 30-year-old fertilizer salesman faces the death penalty if convicted of two counts of murder.
Testimony could be key for prosecution
Dempewolf could be key to the prosecutors' case if she offers an alternative explanation for witnesses who say they saw Laci Peterson walking her dog Dec. 24.
But if Stanislaus County Superior Court Judge Al Girolami determines that the hypnosis techniques amount to hypnotism, strict conditions will have to be met for her testimony to be admissable in court.
Testimony must be limited to matters the witness recalled and related before the hypnosis, and the substance of the pre-hypnotic memory must be preserved in written, audiotape or videotape form before the hypnosis.
The law also requires that the hypnosis be performed by a licensed professional experienced in hypnosis, such as a medical doctor or psychologist, and not done in the presence of law enforcement, the prosecution or the defense.
Defense attorney Mark Geragos indicated in court that the interview had been videotaped, but it is unclear from prosecution documents who used hypnosis techniques on Dempewolf.
Prosecutors also would have to prove by "clear and convincing evidence" at a hearing that the hypnosis did not make the witness's earlier recollection unreliable or "substantially impair" the ability to cross-examine the witness.
Interviewer may lead subject
Hypnosis subjects are susceptible to suggestions -- even subconscious ones -- by their questioner, said Dr. Emily Keram, a forensic psychiatrist at the University of California at San Francisco.
"It's natural for a person to be helpful, and they're prone to give the wrong answers," Keram said. "There may be a question where the interviewer inadvertently demonstrates their need and leads the subject to report things in an effort to address those cues."
Hypnosis, which induces deep relaxation, is effective in reducing anxiety and could be used to calm a witness before he or she is brought out of hypnosis and questioned, Keram said.
There is no evidence that hypnosis improves memory, but there are indications that people later believe more strongly that what they said under hypnosis is accurate, Keram and Spiegel said.
Several prosecutors and defense attorneys said they were unaware of attorneys trying to introduce testimony from hypnotized witnesses since the 1982 Supreme Court case.
"There are so many hoops to jump through, obviously," Los Angeles defense attorney Bradley Brunon said. "The testimony of the witness is potentially unreliable, and there is no way to cross-examine that witness because they are not aware of what is perceived via hypnosis."
Girolami is to address the issue at Peterson's preliminary hearing Oct. 20.
Bee staff writer John Coté can be reached at 578-2394 or email@example.com.