Laci Peterson’s Cause of Death: How Did She Die?

ABC Laci Peterson and Scott Peterson on their wedding day.

Laci Peterson’s remains left few clues to her cause of death when they washed ashore four months after her disappearance. An official cause of death was never determined, but prosecutors argued at trial she was smothered.

Peterson’s body was found badly decomposed, washed up on the San Francisco Bay. An autopsy could not conclusively provide a cause of death. Her body was found separate from the body of her unborn child, who would be named Conner. Laci was eight months pregnant at the time of her death.

The body of Conner, which was largely intact because it was protected in utero, provided a piece of evidence that was key at the Laci Peterson murder trial. Scott Peterson told police he had gone fishing at Brooks Island the day of his wife’s disappearance December 24, 2002. The length of Conner’s leg bone determined he was killed on that day, prosecutors said, according to the appeal filed in Scott Peterson’s case.

ABC 20/20 is revisiting the high-profile case with interviews with Scott Peterson himself and with Amber Frey. Peterson was having an affair with Frey. The new episode, “One Last Chance,” airs at 9 p.m. Eastern time Friday, May 14, 2021.

Here’s what you need to know:

Prosecutors Argued Laci Peterson Was Smothered to Death, But an Official Cause of Death Was Never Determined

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The state’s theory at Scott Peterson’s trial was that Laci Peterson was smothered to death. The defense argued Laci, who was eight months pregnant, was abducted while she was walking her dog, McKenzie. The defense also contended the fetus was cut from her womb and strangled with a string.

Forensic Pathologist Dr. Brian Peterson testified evidence showed the unborn child, who his parents planned to name Conner, died when Laci was killed, according to the SFGate. Dr. Peterson was not related to the family. He performed autopsies on Laci Peterson and Connor Peterson, which washed ashore separately on the San Francisco Bay. While Laci Peterson’s body was badly decomposed, Conner Peterson’s body was largely intact. He surmised this was because he was protected in the uterus. Peterson dismissed the theory that Conner Peterson was strangled. A piece of twine was found wrapped around his neck, but he said it was likely material in the water that happened to become tangled around the body. There was no bruising or other evidence on his body that indicated he was strangled.

“Truly, I believe that for whatever reason Laci met her demise, it was her death that caused the death of (Conner Peterson),” he said, according to the newspaper.

Laci Peterson’s cause of death remains a mystery. Her body was badly decomposed.

“Dr. Peterson speculated she may have died from strangulation or smothering which could leave behind no forensic evidence, but it was impossible to be sure because her head and neck were missing, as well as her forearms, most of both legs and all internal organs, except for the uterus,” the Sioux City Journal reported.

An appeal filed in Scott Peterson’s case said there was no evidence to indicate Laci Peterson was smothered. Law enforcement did not collect pillows to test for evidence. The appeal argued the smothering theory was presented to explain why there was no blood found at their Modesto home.

Conner Peterson, Laci Peterson’s Unborn Child, Was Found More Intact Than His Mother

SAN QUENTIN, CA – MARCH 17: In this handout image provided by the California Department of Corrections, convicted murderer Scott Peterson poses for a mug shot March 17, 2005 in San Quentin, California. Judge Alfred A. Delucchi sentenced Peterson to death March 16 for murdering his wife, Laci Peterson, and their unborn child. (Photo by California Department of Corrections via Getty Images)

Laci Peterson disappeared on Christmas Eve in 2002, and it would be four months before her family would have any inkling what became of her. Even in death, her badly decomposed body left few clues. The body of Conner Peterson was more intact than Laci Peterson, which a forensic pathologist speculated was because the fetus was protected in utero. A late spring storm dislodged the remains of Peterson and her unborn child. Over the course of two days, the remains washed ashore on April 13 and 14, 2003, according to the appeal filed in the Peterson murder case.

Because it was four months before Laci Peterson’s body was found, there was no forensic evidence tying the body to Scott Peterson. The state of California relied on three key pieces of evidence based on testimony from expert witnesses. An expert in fetal growth testified evidence indicated the unborn child, Conner, was killed December 23 or 24. The evidence was collected from Conner’s leg bone. Another witness testified to dog scent evidence. A dog alerted at the Berkeley Marina, indicating Scott Peterson transported his wife’s body to the marina. Thirdly, a hydrologist testified to body movement in the bay. The witness said Laci Peterson’s body was left exactly where Scott Peterson told police he was fishing.

Prosecutors argued at trial Scott Peterson killed his wife at their Modesto home. However, according to the appeal filed in his case, no evidence of a murder was found at the house.

“No blood, urine, or tissue of any kind was found at the house. Officer Letsinger noted there were no signs of “foul play” at the Peterson home. Nor did Karen Servas – – the Peterson’s next door neighbor — hear screams or other suspicious noises coming from the house on the night of the 23rd or the morning of the 24th. Finally, there were no defensive marks or wounds on Scott at all,” the appeal said.

Police spotted a mop and two buckets outside the home, which they surmised Peterson used to clean up the crime scene. But nothing of evidentiary value was found on the mop or buckets, the appeal said.

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