Man Who Killed His Brother In Princeton Apartment Found Dead In Jail

PRINCETON, NJ — The man who killed his younger brother at their Princeton apartment last year died earlier this month.

Matthew Hertgen, 32, was found dead on May 8 in Mercer County jail. Matthew died in an apparent suicide, authorities told NJ.com. An autopsy report is pending.

Matthew had been in custody since February 2025, when he called 911 to report the death of his brother Joseph Hertgen, 27, at the brothers' Michelle Mews apartment in Princeton.

On March 19, Mercer County Superior Court Judge Robert Lytle found Matthew not guilty by reason of insanity, concluding he was legally insane at the time of the crime — a determination prosecutors said they could not contest.

At the March hearing, forensic psychologist Dr. Gianni Pirelli testified that Matthew had been diagnosed with schizophrenia and had struggled with severe mental illness since 2021. Pirelli told the court that at the time of the killing, Matthew believed he was Jesus Christ and that an apocalypse was imminent. "Anytime he closes his eyes, he's seeing tremendous visions," Pirelli testified.

On the evening of Feb. 22, 2025, Hertgen had spent hours with a third brother, identified in court records only as "D," who told investigators Matthew had been "distressed, despondent, and experiencing terrifying visions" throughout the day. D dropped Matthew off at the apartment around 10 p.m., briefly meeting Joseph before leaving. Less than 90 minutes later, Matthew called 911.

Officers arriving at the scene found Joseph on the floor in a pool of blood, with severe blunt force trauma and deep lacerations. A golf club lay near the body. When detained, Matthew told police he had "gone into a fit of madness, maybe like forty minutes ago." Joseph, who graduated from Toms River North in 2016, had worked as an analyst for Locust Point Capital in Red Bank since 2023.

His family, in an obituary, remembered a different man — one shaped by faith, intellect, and love, whose final years were consumed by illness.

"Growing up, Matthew is remembered as a caring and loving person," the obituary read. "He was blessed with a large and extended family who he enjoyed spending time with."

Matthew attended Wesleyan University in Connecticut, where he played soccer and graduated with a Bachelor of Arts in microbiology and biochemistry. He went on to serve as a vice president in a senior finance capacity at a telecom company for many years.

"During his later years, Matthew struggled with severe and profound mental health issues; yet he expressed sorrow, remorse, and repentance in many ways," his family wrote. "He departed with the love, friendship and forgiveness of his family and the eternal hope of salvation. May he rest in peace."

If you or someone you know is struggling with mental health, call or text 988 to reach the Suicide and Crisis Lifeline.

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