So-called "cult mom" Lori Vallow is set to stand trial for the October 2019 murders of her two children and her husband's ex-wife on April 3.
Her defense team will have to address questions of an unknown killer to prove Vallow's innocence after she was found competent to stand trial.
"It's not unusual … to raise an alternate suspect defense," Richard Robertson, a private investigator hired to work Vallow's case in 2019, told Fox News Digital. "We refer to it as the SODI defense — some other dude did it."
While many of the most prolific murder suspects and convicted killers have pleaded not guilty by reason of insanity, the following five defendants and their defense teams have pointed fingers at unknown assailants in their efforts to prove innocence.
Alex Murdaugh, a disgraced South Carolina personal injury lawyer, was convicted on March 2 of the June 2021 murders of his wife and son.
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"I respect this court, but I’m innocent," Murdaugh said when he took the stand in his own trial in February. "I would never under any circumstances hurt my wife Maggie, and I would never under any circumstances hurt my son, ‘Paw Paw.’"
In video evidence presented in court, Murdaugh implicated his groundskeeper in Maggie and Paul's murders, but a jury ultimately decided that discovery presented in court was enough to sentence him to serve life in prison.
In one of the most widely televised criminal trials in the United States, former NFL star O.J. Simpson was accused of killing his wife, Nicole Brown Simpson, and her friend Ron Goldman in 1994. He was acquitted in 1995.
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"I did not, could not and would not have committed this crime," Simpson said when he initially pleaded not guilty to the murders in 1995.
Part of his defense team's strategy included evidence showing a botched crime scene, problematic DNA evidence and a pair of leather gloves found at the crime scene that his attorneys argued were worn by an unknown assailant who killed Brown Simpson and Goldman. Simpson squeezed into a new pair of gloves similar to those found at the scene during his trial.
"If it doesn't fit, you must acquit," his attorney, John Cochran, famously said at the time.
Scott Peterson was convicted in 2004 for the murders of his 27-year-old wife, Laci, and their unborn son, Conner. Prosecutors argued at the time that he killed Laci and disposed of her body on Christmas Eve 2002 in San Francisco Bay.
The California Supreme Court overturned Peterson’s death sentence in 2020 after news that prospective jury candidates were improperly dismissed came to light, but the court maintained his conviction.
The case is far from over, according to Peterson's lawyers, suggesting an unknown suspect killed Laci and Conner.
"Just in the last few months, we have learned new information that will prove Scott Peterson did not murder his wife, Laci," attorney Pat Harris told Fox News Digital in a December 2022 statement. "And we are going to continue to push forward until he is freed."
Deceased New York real-estate tycoon Robert Durst was convicted in September 2021 for the murder of his best friend, Susan Berman, in 2000. He was sentenced to life in prison without parole and died in January 2022.
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Prior to his death, he was long suspected of killing his wife, Kathie Durst, who vanished in 1982. Prosecutors allege that the millionaire attempted to silence Berman because she helped him cover up Kathie's disappearance.
Durst took the stand in his own trial for three weeks and repeatedly testified that he did not know who killed Berman.
He did admit under cross-examination, however, that he would lie under oath in order to get out of trouble.
"‘Did you kill Susan Berman?’ is strictly a hypothetical," Durst said from the stand. "I did not kill Susan Berman. But if I had, I would lie about it."
Both Vallow and her husband are accused of killing 17-year-old Tylee Vallow and 7-year-old J.J. Vallow in 2019.
They were initially scheduled to stand a joint trial in 2021, but proceedings have been delayed due to Vallow's competency examinations and an "exceptionally voluminous" collection of evidence, among other factors. Judge Steven Boyce ruled in February that their cases would be severed because Vallow has refused to waive her right to a speedy trial.
Their defense teams are expected to argue that the couple did not kill their children, suggesting that an outside party did. Additionally, while the couple has not blamed one another for the crimes, Robertson says it is not out of the question.
"What I don't know is whether Chad is going to be testifying [in Vallow's trial]. … He's in a great position to cooperate against Lori," the private investigator explained.
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Authorities arrested Vallow in February 2020 and Daybell in June 2020.
The Fremont County grand jury initially issued indictments against Vallow and Daybell in May 2021 on two counts of first-degree murder in connection with Tylee and J.J.'s deaths. The two children disappeared in September 2019.
They were missing for months when police say the couple lied about the childrens' whereabouts and then slipped away to Hawaii before the childrens' bodies were found in 2020 buried on Daybell's property in rural Idaho.
Vallow and Daybell, who married in November 2019, allegedly collected J.J.'s and Tylee's Social Security benefits between Oct. 1, 2019, and Jan. 22, 2020, after their murders.
The couple were indicted in late May 2021 on multiple counts each of conspiracy to commit first-degree murder and grand theft by deception, first-degree murder and conspiracy to commit first-degree murder related to the deaths of Tylee, J.J. and Chad Daybell's ex-wife, officials announced at the time. Arizona officials in June 2021 also indicted Vallow in the July 2019 murder of her ex-husband, Charles Vallow.
Daybell has written several apocalyptic novels based loosely on Mormon theology. Both were involved in a group that promotes preparedness for the biblical end times. Vallow and Daybell bonded over their religious beliefs after initially meeting in 2018, when they appeared together for the first time on a podcast discussing theories about the end of the world.
The Associated Press contributed to this report.
