The preppy Princeton cannibal killer — who was found not guilty by reason of insanity — was discovered dead in his New Jersey jail cell in an apparent suicide.

Matthew Hertgen was found dead at Mercer County Jail on May 8, the Mercer County Prosecutor’s Office told NJ.com. The outlet revealed the news on Friday.

An official cause of death has not been released.

Hertgen had previously attempted to hang himself in his cell at Mercer County Jail just one week after his arrest in February 2025.

The 31-year-old was ruled not criminally responsible for his brother’s murder by reason of insanity by Mercer County Superior Court Judge Robert Lytle on March 19.

The former Wesleyan soccer player stabbed and beat his younger brother to death with golf clubs in their upscale apartment in February 2025. He then ripped out his brother’s eyeball and ate it. Hertgen also set the family cat on fire after the killing.

Joseph Hertgen’s body, 26, was found by police lying in a pool of blood next to a bloody knife.

Surveillance footage presented at Hertgen’s trial showed him tackling his brother to the ground and assaulting him.

According to forensic psychologist Dr. Gianni Pirelli, the cannibalistic killer suffered from “prophetic and divine visions.” He was diagnosed with schizophrenia and, at various times, believed himself to be Jesus Christ, the Antichrist, God, or to possess multiple souls.

“Anytime he closes his eyes, he’s seeing tremendous visions,” Pirelli testified.

Hertgen also believed the world was on the brink of the apocalypse and that only a “sacrificial murder” could save it. He was heavily influenced by a chapter in Swiss psychologist Carl Jung’s Red Book titled “The Sacrificial Murder.”

“It kind of clicks for him and he puts two and two together,” Pirelli said.

Hertgen’s mental health issues began while he was living in New York City in 2021. He had enjoyed an idyllic childhood, growing up with his brothers in a $1.1 million home in Toms River before the family moved to the luxurious Michelle Mews apartments.

In his obituary, his family remembered the man as a “caring and loving person.”

“During his later years, Matthew struggled with severe and profound mental health issues; yet he expressed sorrow, remorse, and repentance in many ways,” the obituary stated.