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 likely had a mental health breakdown that ultimately destroyed his family, according to a legal expert.

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.

One of Matthew Hertgen’s friends from Toms River High School told Fox News Digital that he has “nothing bad to say” about the former soccer player, who went on to study at Wesleyan University in Connecticut. Joseph Hertgen also played soccer at Toms River before he was recruited to the University of Michigan.

“He was just a cool kid who played soccer, got good grades, funny,” the friend said, adding that “Matt was a cool guy” and the recent news “just doesn’t sound like him.”

Princeton police initially responded to a 911 call on Feb. 22 at around 11:16 p.m. reporting a fire and a dead body at the Michelle Mews Apartments complex. (University of Michigan | Wesleyan University | Google Maps)

Gotlin said that while it’s uncommon for people from affluent families to descend into a mental health crisis that ends in death, it is not unheard of. He mentioned the case of Luigi Mangione, the suspect accused of killing UnitedHealthcare CEO Brian Thompson in December on a sidewalk in Manhattan.

Mangione graduated valedictorian from the Gilman School, a private all-boys high school in Baltimore, in 2016. He went on to receive his bachelor’s and master’s degrees in computer science from the University of Pennsylvania in 2020.

An empty courthouse is seen as lawyers convene and Judge Gibbs presides over the Matthew Hertgen murder hearing by video conference at the Mercer County Criminal Court on Feb. 27, 2025, in Trenton, N.J. (Stephanie Keith for Fox News Digital)

“It’s not common, but the best example of it is Luigi Mangione. He grew up, went to the best schools, private schools … and he’s obviously mentally ill,” Gotlin said. “There’s no question about it. People get sick. Mental illness is something, unfortunately, the medical industry hasn’t really conquered.”

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.

An investigation into Joseph’s death is ongoing.