The New Jersey man accused of killing and mutilating his younger brother — and later ruled not guilty by reason of insanity — has died behind bars in what authorities believe was an apparent suicide.
According to the New York Post, Matthew Hertgen was found dead on May 8 inside his cell at Mercer County Jail, the Mercer County Prosecutor’s Office announced.
Officials have not publicly released the official cause of death.
Hertgen had previously attempted suicide shortly after his February 2025 arrest, when authorities said he tried to hang himself inside the jail.
The shocking case drew national attention after prosecutors accused Hertgen of carrying out a gruesome attack on his 26-year-old brother, Joseph Hertgen, inside the family’s New Jersey residence.
Police responding to the scene discovered Joseph’s body lying in a pool of blood near a knife, according to investigators.
Authorities also alleged that Hertgen set the family cat on fire during the violent episode.
During court proceedings, surveillance footage reportedly showed the brothers struggling before the fatal attack unfolded.
Mental health testimony later became central to the case.
Forensic psychologist Dr. Gianni Pirelli testified that Hertgen suffered from schizophrenia and experienced disturbing delusions and hallucinations.
According to Pirelli, Hertgen believed at different times that he was Jesus Christ, the anti-Christ, God, or someone possessing multiple souls.
“Anytime he closes his eyes, he’s seeing tremendous visions,” Pirelli testified during the proceedings.
Pirelli also told the court that Hertgen became heavily influenced by Swiss psychologist Carl Jung’s “Red Book,” specifically a chapter titled “The Sacrificial Murder.”
“It kind of clicks for him and he puts two and two together,” Pirelli said.
The court ultimately determined Hertgen was not guilty by reason of insanity.
Testimony during the trial indicated Hertgen’s mental health struggles intensified several years earlier while he was living in New York City in 2021.
Before the tragedy, Hertgen reportedly came from a wealthy New Jersey family and spent his childhood growing up in Toms River alongside his brothers.
The family later relocated to the upscale Michelle Mews apartments.
Despite the horrific allegations against him, Hertgen’s family remembered him in his obituary as someone whose life became consumed by severe mental illness.
“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.
The case stunned many in New Jersey because of both the brutality of the killing and the testimony describing Hertgen’s deteriorating mental state.
Authorities have not released additional details surrounding the circumstances of his death inside the jail.
