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Matthew Hertgen, known for the tragic incident involving his brother’s death in 2025, has passed away.
The Mercer County Detention Center in Hopewell, New Jersey, reported that Hertgen died by apparent suicide on May 8, according to a representative from the prosecutor’s office speaking to Oxygen. The official autopsy results are still awaited.
Back in March, Hertgen was declared not guilty by reason of insanity for the killing of his 26-year-old sibling, Joseph. Prior to this ruling, he had entered a plea of not guilty.
The grim series of events began on February 22, 2025, when Matthew made an emergency call to 911.
During the call, Matthew informed the operator that Joseph was deceased in his Princeton apartment, which had also been the site of a fire. He declined to give additional information, as noted in an affidavit of probable cause accessed by Oxygen.
Responding officers were met by Matthew at the front door before discovering Joseph’s body inside the apartment.
Joseph lay on the dining room floor with a large pool of blood around his head and torso, per the affidavit. He appeared to have sustained blunt force trauma to the back of his head and a large laceration on his chest and abdomen, “which exposed his chest cavity.”
Joseph had lacerations to his right eye, and his right eyeball was not visible, according to the affidavit.
A bloody golf club lay near the body, along with a cup full of what officers believed was blood and a plate and eating utensils, which were both blood-smeared.
When officers entered the living room, they discovered a dead cat on an ottoman. The animal appeared to have suffered blunt force injuries and burns.
When Matthew was asked why his hands were lacerated, he allegedly explained that he had gone “into a fit of madness…maybe like, 40 minutes ago.”
Matthew was arrested and charged with first-degree murder, four weapons offenses and third-degree animal cruelty. Police later found a knife in his possession, according to an indictment viewed by Oxygen.
According to Matthew’s other brother, who spent time with him in the hours leading up to the killing, Matthew had struggled with severe mental illness for the previous five years. The brother also told police in the affidavit that earlier that day, Matthew was “extremely distressed, despondent, and experiencing terrifying visions.”
The brother said that the two had gone to the grocery store, then returned to Matthew’s apartment, where he briefly entered and saw Joseph.
Later that evening, the brother texted Joseph to say Matthew had been “struggling with visions,” per the affidavit, and asked Joseph to contact him if he needed help.
Joseph allegedly replied, “Will do,” but did not respond to any follow-up messages.
During Matthew’s one-day bench trial, forensic psychologist Dr. Gianni Pirelli stated Matthew had been diagnosed with schizophrenia. The brain disorder is a condition that can include symptoms of delusions and hallucinations, according to the American Psychiatric Association.
“He is one of the most severe cases of mental illness that I’ve seen of someone who can still hold a conversation,” Pirelli said, according to NJ.com. He added that Matthew suffered from “religious, supernatural and apocalyptic visions and beliefs;” and not that Matthew also believed he harbored more than one soul, including God.
Judge Robert Lytle responded that, based on Pirelli’s testimony, it seemed that Matthew had been “required to commit an act of evil, an act of evil to prevent spiritual catastrophe and save his soul.”
Matthew did not “experience his actions as ordinary homicide,” Lytle said in part, according to NJ.com. “Within his psychotic framework,” said Lytle, “he believed that he was engaged in a spiritually necessary act to prevent an eternal damnation.”
A court hearing scheduled at the end of May would have sentenced Matthew to a state psychiatric facility, the spokesperson told Oxygen.