Matthew Hertgen, who killed his brother Joseph last year, has died in a New Jersey jail

Matthew Hertgen, the man who attracted widespread attention following the killing of his younger brother and a cat in 2025, has died.

The former college football player passed away at Mercer County Jail on 8 May, the Mercer County Prosecutor's Office confirmed to NJ.com. He was 32 years old, according to his obituary.

Matthew was discovered dead in the New Jersey facility in what appeared to be a suicide. His official cause of death remains pending the outcome of an autopsy, NJ.com reported.

The Wesleyan University graduate had previously attempted to take his own life approximately one week after his arrest in February 2025, the New York Post reported.

The judge ruled Matthew legally insane in March

Matthew's death follows a March ruling in which a judge determined he was not legally responsible for the death of his 26-year-old brother, Joseph Hertgen, who was killed on 22 February 2025, due to severe mental illness, NJ.com reported.

The judge accepted the insanity defence and had scheduled a May hearing to determine Matthew's future custody arrangements.

A forensic psychologist testified to escalating psychotic behaviour

The New Jersey native had a documented history of deteriorating psychotic behaviour, forensic psychologist Dr Gianni Pirelli testified in court.

Dr Pirelli told the court that Matthew had experienced "prophetic and divine visions" of a religious and apocalyptic nature, at times believing himself to be God or the anti-Christ, or that a "sacrificial murder" was required to save the world, according to the New York Post.

"Anytime he closes his eyes, he's seeing tremendous visions," Pirelli said of Matthew whilst testifying, per the outlet.

Matthew faced a murder charge over the Princeton apartment attack

Matthew faced a first-degree murder charge and weapons offences in connection with his brother's death, which took place at a Princeton, New Jersey, apartment. He also faced an animal cruelty charge relating to the killing of a cat that resided at the property.

He was accused of attacking Joseph with a knife and a golf club before removing his eye and setting fire to the animal. He also consumed his brother's eyeball, per the New York Post.

A plate and utensils smeared with blood, along with a small cup containing what appeared to be blood, were recovered from inside the home, per a probable cause affidavit previously reviewed by PEOPLE.

Older brother had warned Joseph on the night of the killing

During the course of the investigation, officials spoke with Matthew and Joseph's older brother, David Hertgen, who informed them that Matthew had been experiencing severe mental illness for five years and had been "extremely distressed, despondent and experiencing terrifying visions" on the day of Joseph's death, per the affidavit.

On the night of the killing, David sent Joseph a text message warning him that Matthew was having "visions" and asking him to get in touch if he required assistance. Joseph responded, "Will do," according to the affidavit.

Family remembers Matthew as a caring person before mental illness took hold

In his obituary, Matthew's loved ones emphasised his struggles with mental health whilst also reflecting on the person he had been in earlier life.

The family also encouraged donations to NAMI Mercer, a non-profit organisation supporting Mercer County, New Jersey residents affected by mental illness.

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

"Matthew attended Wesleyan University in Connecticut, where he played soccer and graduated with a Bachelor of Arts degree in microbiology and biochemistry. He went on to work as VP in a senior finance capacity for 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," the obituary continues.

"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 challenges, emotional distress, substance use problems, or just needs to talk, call or text 988, or chat at 988lifeline.org, available 24 hours a day, seven days a week.