Supreme Court of California Affirms Death Sentence of Young Adult Defendant After Testimony on the Effects of Childhood Trauma on Brain Function

California Supreme Court (link)

The California Supreme Court affirmed the conviction and sentence of Run Peter Chhoun, who had received a death sentence for the murder of multiple victims during a home invasion robbery in 1995. He argued that the trial court abused its discretion by admitting evidence of uncharged murders and his gang affiliation and by failing to instruct the jury to consider his psychological immaturity.

Chhoun was born in Cambodia and experienced violence and starvation after being sent to a work camp at four years old. When he was nine, he reunited with his family and immigrated to America, where he struggled at a school that was not equipped to handle refugees or offer language support.

Chhoun “found acceptance and trusted friends” when he joined the Tiny Rascals Gang, which consisted of members from age 11 to 25. When he was 22, he and four other members robbed the Nyugen family. During the robbery, Chhoun killed five members of the family and wounded the only survivor, a three year old boy.

At trial, the prosecution brought evidence related to Chhoun’s gang affiliation and his involvement in earlier, similar murders and drive-by shootings. Chhoun had been linked to these crimes, but not yet charged.

The defense called on experts in trauma and cross-cultural psychiatry to testify on the impacts of Chhoun’s childhood on his development. One expert diagnosed Chhoun with PTSD and testified that his criminal behavior was an “artifact of survival strategies developed in Cambodia.” Other experts testified that malnutrition and lack of familial support had delayed his brain development. Despite this evidence, he was convicted of multiple counts of murder and robbery and sentenced to death.

The appellate court disagreed with Chhoun’s contention that evidence related to his gang affiliation and prior uncharged criminal conduct was irrelevant, asserting that his position in the gang as a “shot caller” “meant he had enough standing in the gang to give direction to junior members” and that evidence related to similar uncharged crimes had been properly admitted to “show the defendant’s state of mind.”

The court further held that the jury’s instructions as a whole had allowed the jury to consider Chhoun’s age and psychological immaturity as mitigating factors. Accordingly, the court affirmed Chhoun’s conviction and death sentence.

Citation: People v. Chhoun, 11 Cal.5th 1 (2021)

Key words: adolescent brain, young adult, adverse childhood experiences, PTSD, death sentence

This post is the 104th post as part of an ongoing Center for Law, Brain & Behavior (CLBB) series tracking the latest developments in law and neuroscience cases. To see previous posts about recent cases, see the full case archive on the CLBB website. To see updates on legal scholarship, see the Neurolaw News, hosted by the MacArthur Foundation Research Network on Law and Neuroscience. This project is made possible through support of the Dana Foundation.




at Mass General Hospital, Harvard Medical School

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Center for Law, Brain & Behavior

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at Mass General Hospital, Harvard Medical School

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