06/01/2026
MARCH 18 INSANITY RULING UPDATE: Matthew Hertgen, 32, the New Jersey man found not guilty by reason of insanity after killing his younger brother in a brutal Princeton apartment attack, has been found dead in jail.
Hertgen died on Friday, May 8, at the Mercer County Correction Center in Hopewell Township, New Jersey. Court TV reported that jail officials confirmed his death and said it is being treated as an apparent su***de, but the official autopsy report had not yet been completed.
The case goes back to February 22, 2025, inside the brothers’ apartment at Michelle Mews in Princeton, New Jersey.
Prosecutors said Matthew Hertgen, then 31, called 911 and reported a fire and a dead body inside the apartment. When police arrived, they found Matthew inside the residence with the body of his younger brother, Joseph Hertgen, 26.
Joseph was pronounced dead at the scene. Authorities said he had blunt force trauma and lacerations. Prosecutors said Matthew used a knife and a golf club in the attack. Investigators also said the family cat had been beaten, stabbed, and set on fire.
The details that came out later were horrifying. Court TV reported Joseph was found with a large pool of blood around his head and torso, his chest cavity exposed, and his right eye missing. People reported that Matthew was accused of removing and eating his brother’s eyeball.
Matthew Hertgen was originally charged with first-degree murder, weapons offenses connected to the knife and golf club, and third-degree animal cruelty in the death of the cat.
But on March 18, 2026, Mercer County Superior Court Judge Robert Lytle found Matthew not guilty by reason of insanity. The ruling meant the court found he killed Joseph, but was not criminally responsible because of his mental state at the time.
A forensic psychologist, Dr. Gianni Pirelli, testified that Matthew had schizophrenia and had struggled with serious mental illness since at least 2021. Reports said his symptoms included delusions, hallucinations, and religious and apocalyptic visions.
Matthew was supposed to return to court on May 29 for a hearing about his mental health status and the next steps, including transfer to a psychiatric hospital. He died before that hearing happened.
This case is beyond disturbing. A young man lost his life in an attack so violent it shocked people across the country. A family lost two sons in two different ways. And the court record also shows how severe untreated or worsening mental illness can become when warning signs turn into danger.
Mental illness does not excuse the horror of what happened to Joseph. It also cannot be ignored when a person is spiraling, making threats, seeing visions, becoming violent, or frightening the people around them. Families should not be left alone to manage that kind of danger behind closed doors.
Joseph Hertgen was 26. He was a former University of Michigan soccer player. He should still be alive.
Sources: Mercer County Prosecutor’s Office, Court TV, People, CentralJersey.com, Middletown Press.