Princeton man found not guilty of murder by reason of insanity

⚖️ Princeton man found not guilty by reason of insanity in brother’s killing

⚖️ Psychologist testified defendant had severe schizophrenia and “visions”

⚖️ He will likely be committed to a secure psychiatric facility after sentencing

TRENTON — A Princeton man accused of brutally murdering his younger brother — and the family’s cat — was in court Wednesday for a one-day bench trial.

Matthew Hertgen appeared before Superior Court Judge Robert Lytle, who found the defendant not guilty by reason of insanity.

The now 32-year-old Hertgen has been in custody since his arrest after brutally killing Joseph Hertgen last year.

Mental illness and schizophrenia at center of defense

Just one witness testified, a clinical and forensic psychologist who said that Matthew Hertgen was schizophrenic and had struggled with his mental health since 2021, Court TV reported.

“I think it’s important for me to say that when I saw him, and based on my record review, he has one of the most severe mental illnesses that I’ve seen,” Dr. Gianni Pirelli testified.

Hertgen suffered from frequent “visions,” including delusions and hallucinations that often took religious and apocalyptic overtones, Court TV reported.

Under state law, a defendant found not guilty by reason of insanity is typically committed to a psychiatric facility and remains under court supervision.

There are typically periodic reviews to determine whether the person poses a danger to themselves or others.

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Matthew Hertgen on March 24, 2025 for Mercer County Superior Court (via njcourts.gov)

Grisly details emerge from 911 call and crime scene

Court documents obtained by New Jersey 101.5 show Matthew Hertgen called 911 after 11 p.m. on Feb. 22, 2025, and said the victim had been dead for 30 to 40 minutes.

He reported a fire and his brother’s dead body in his home at the Michelle Mews luxury apartments.

When asked how Joseph Hertgen was hurt, Matthew Hertgen said, “I’m not gonna go into any more details right now.”

The 27-year-old victim had suffered extensive head and body injuries and was lying in a pool of blood when police arrived, according to court documents.

He was found next to blood-covered dinnerware, and his right eye appeared to have been cut out.

Matthew Hertgen was also accused of burning and killing the family’s pet cat.

Arresting officers said that Hertgen’s hands were covered in cuts and scratches.

Family warned of “visions” hours before killing

Investigators spoke to other family members, and a third brother told police that Matthew Hertgen had suffered from “severe mental illness” for the past five years.

He said earlier on Feb. 22, 2025, the defendant was “extremely distressed, despondent, and experiencing terrifying visions.”

The surviving brother said he picked up Matthew Hertgen around 4:30 p.m. and after spending time together, he dropped him back off at the Michelle Mews residence around 10 p.m.

At that point, Joseph Hertgen was home and seen alive by the surviving sibling, the affidavit said.

After leaving, the other Hertgen sibling sent a text message to Joseph, saying that Matthew was having trouble with “his visions” and to reach out for help.

He also texted Matthew Hertgen just before 10:30 p.m., inviting him on a hike the next day and saying “hang in there,” according to the affidavit — the defendant did not text back.

Joseph Hertgen was killed in his family's Princeton home (Credit Legacy com by Silverton Memorial Funeral Home)

Victim remembered as kind, with a "great love of life"

The victim was mourned by his parents, other relatives and a "large and loving extended family."

"He was such a kind person, had a great love of life and his smile brightened every room," according to an online obituary for Joseph Hertgen.

Following Wednesday’s trial, Hertgen’s sentencing was scheduled for May 1 — at which point he was expected to be sent to a secure facility.

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