New Jersey man found dead in Mercer County jail after being ruled legally insane in brother’s killing
Matthew Charles Hertgen died on May 8 at the Mercer County Correction Center in Hopewell Township in what authorities ruled as an apparent suicide. Officials said the final autopsy report is still pending.
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A New Jersey man who was found legally insane after killing his younger brother during what doctors described as a severe mental health crisis has died in custody, Mercer County officials confirmed.
Matthew Charles Hertgen died on May 8 at the Mercer County Correction Center in Hopewell Township in what authorities ruled as an apparent suicide. Officials said the final autopsy report is still pending.
Hertgen had been at the center of a high-profile case that shocked Princeton and drew attention across New Jersey earlier this year.
Police said Hertgen killed his younger brother, Joseph Hertgen, inside the brothers’ Princeton apartment in February 2025. Prosecutors alleged the attack involved a knife and a golf club. Authorities also said a family cat was killed during the incident.
During court proceedings, mental health experts for both the prosecution and defense agreed Hertgen suffered from schizophrenia and severe delusions.
In March 2026, a Mercer County judge ruled he was legally insane at the time of the killing, meaning he would be committed to a psychiatric facility instead of serving a traditional prison sentence.
Court records and testimony described Hertgen as someone who experienced hallucinations, religious delusions and what he allegedly called a “fit of madness” leading up to the attack.
Officials have not released additional details about the circumstances surrounding Hertgen’s death inside the correctional facility. It is also unclear whether he had been under a suicide watch or receiving mental health monitoring at the time.
The Mercer County Prosecutor’s Office and correctional officials have not announced whether an internal investigation is underway.
