The Princeton, New Jersey, man known as a star student in high school who is now accused of killing his brother and a family cat allegedly told police he had a “fit of madness” when they responded to the scene of the crime, according to court records obtained by local news outlets.
Matthew Hertgen, 31, is accused of murdering his 26-year-old brother, Joseph Hertgen, in the family’s Princeton apartment, allegedly with a knife and golf club. He is also charged with animal cruelty related to the death of a cat.
Princeton police initially responded to a 911 call from Matthew on Feb. 22 around 11:16 p.m. reporting a fire and his brother’s dead body at the Michelle Mews Apartments complex.
When a dispatcher asked Matthew how his brother was injured, he said, “I’m not gonna go into any more details right now,” a probable cause statement obtained by NJ.com reads.
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Matthew Hertgen is accused of murdering his younger brother and a cat in their Princeton, New Jersey, apartment. (University of Michigan/ Mercer County prosecutor/ Google Maps)
Police arrived and found Matthew in the residence along with his brother’s body, which had significant injuries to the head — including a missing eye — as well as injuries to Joseph’s chest and upper body. Police also found a cup of blood with utensils and a plate, NJ.com reported, citing the probable cause document.
While interviewing Matthew, who apparently had cuts on his hands, he told police he “went into a fit of madness… maybe like forty minutes ago.”
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Joseph and Matthew Hertgen’s high school yearbook photos.
Homicide detectives also interviewed Matthew’s other surviving brother, who told police the 31-year-old suspect had struggled with mental health issues for about five years.
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The brother had seen Matthew earlier in the day, when he had been experiencing a depressive episode and “terrifying visions,” the brother told police, according to NJ.com.
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Matthew Hertgen is accused of murdering his younger brother and a cat in their Princeton, New Jersey, apartment. (Facebook)
The gruesome details in the probable cause statement will likely be discussed during Matthew’s detention hearing at 11 a.m. EST Thursday, according to David Gelman, CEO of Gelman Law and a former prosecutor in New Jersey.
“It’s very disturbing. You don’t see many murders like this,” Gelman told Fox News Digital. “You can see it’s very personal.… I was a prosecutor and I dealt with a ton of murders… and as a defense attorney, I also deal with murders. And when you see these types of really gruesome, graphic, heinous crimes… I have a feeling that this individual definitely has some type of mental illness.”
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From left, David Hertgen, Debra Hertgen and David Hertgen Jr. attend the funeral for Joseph Hertgen at St. Luke Roman Catholic Church on Saturday, March 1, 2025, in Toms River, New Jersey. Joesph was allegedly killed by his brother, Matthew, in their Princeton apartment on Feb 22. (Stephanie Keith for Fox News Digital)
He described a detention hearing as “like a mini trial.” New Jersey does not have bail, so the hearing is to determine whether Matthew is a big-enough threat to the public that he should remain behind bars. The prosecution and the defense will both bring certain evidence forward.
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“I was a defense attorney, I wouldn’t fight it. I would say, you know what? We think there’s a mental issue,” Gelman said.
The public defender’s office, which is representing Hertgen, told Fox News Digital that its attorneys do not comment on pending cases.
Matthew Hertgen appears in court for a detention hearing on Feb. 27. (Mercer County)
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Joseph Hertgen was pronounced dead at the scene, and his autopsy results are pending. Local and state officials are investigating the 26-year-old’s death as a homicide.
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Joseph and Matthew Hertgen were star soccer players in high school and college. They were both athletes at Toms River High School, and Matthew went on to study at Wesleyan University in Connecticut. Joseph Hertgen was recruited to play soccer at the University of Michigan.
