DNA taken from the mouth of a former police detective so closely matched saliva from a bite mark on the arm of a murdered woman that no one else could have produced that genetic similarity, a criminalist told jurors Friday.

Los Angeles Police Department scientist Jennifer Francis, who analyzed evidence in the 26-year-old murder case, offered a conclusion that bolstered prosecution claims that defendant Stephanie Lazarus murdered her romantic rival.

Francis said the DNA of Lazarus was found on the bite mark discovered on victim Sherri Rasmussen's body after she was slain in 1986.

The case lay dormant and was reopened after two decades, with DNA analysis credited with reviving the case and implicating Lazarus.

The 51-year-old Lazarus, once a decorated LAPD investigator, listened attentively as Francis provided the strongest evidence against her.

Lazarus has pleaded not guilty and her lawyer, Mark Overland, has suggested that the DNA swabs taken at the time of Rasmussen's killing were corrupted over the years and are not reliable evidence.

Prosecutors claim that Lazarus was consumed with jealousy when her longtime lover, John Ruetten, announced he had decided to marry Rasmussen, a nursing supervisor at a hospital. When Rasmussen was killed, investigators believed she was the victim of a home invasion robbery.

Lazarus' name came up when the case was reopened and new detectives looked at the facts. Other police witnesses have told how they followed Lazarus surreptitiously and collected her DNA from a cup she discarded during a shopping trip.

It provided a partial match to DNA from the bite, they said. But it wasn't until Lazarus provided a DNA sample from her mouth while in custody that they had a perfect match, they said.

Francis described how she received swabs for testing that had been placed in an envelope a quarter century before. She identified pictures of the envelope which she said was in "ratty" condition and had at least one large tear. A photo projected on a courtroom screen showed a test tube top sticking out of a tear in the envelope. Francis said she also cut a slit in the envelope to remove the tube.

That has led to claims of evidence tampering by the defense.

During cross-examination by Overland, Francis said DNA evidence is highly susceptible to contamination and degradation over time. But she said laboratories have controls to prevent that.

She also testified that she was first approached to analyze materials in the case in 2004. In early 2005, she determined the person who made the bite mark was probably a female.

For unexplained reasons, the case then sat dormant again until 2009, when a detective reopened it and Francis compared the genetic profile of the biter with the DNA sample taken from Lazarus' mouth.

Under questioning by Deputy District Attorney Paul Nunez, Francis said the genetic profile of Lazarus and the bite mark would be expected to be found in one in 402 quadrillion individuals.

"On our Earth would you expect to find another individual with the profile of Stephanie Lazarus and Exhibit 30 (the bite)?" Nunez asked.

"No," said the witness.

The trial is in recess until Tuesday. Monday is a court holiday.

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Witness: LA Detective's DNA Matched Bite Mark