A 35-year-old Illinois State Trooper found in his squad car with a single gunshot wound on Friday died by suicide, the Cook County Medical Examiner’s office told The Associated Press.

Illinois State Police said they’d opened an investigation into the death of George Mason after finding him in his parked vehicle around 1:42 p.m. local time on northbound Interstate 94 at 43rd street.

He was transported to the University of Chicago hospital but died shortly thereafter.

“It is with profound heartache and unfathomable sadness that we inform you of the death of Trooper Gerald Mason. Trooper Mason was one of the many fearless Troopers assigned to ISP District Chicago. We are asking the public to respectfully give consideration to the family of Trooper Mason and the whole ISP family while we continue to grieve and work through this tragedy,” Director Brendan Kelly said in a statement.

Mason, an 11-year veteran of the ISP, was on duty at the time of the shooting, ABC Chicago station WLS reported.

“Many people called Mason ‘The Hulk.’ He was a solid, strong man. He even ripped his trooper pants during a foot pursuit because of those big muscles,” Kelly said in a press conference Friday evening.

Kelly highlighted the challenging work troopers face day in and day out.

“The amazing men and women that we all ask to do so much, again and again and again, may seem like superheroes on many days, but they’re not immortal. They’re not indestructible. They are human beings with hearts, minds and souls as fragile as the next person. They have a breaking point,” Kelly said.

Linda Mason, the trooper’s mother, was heartbroken.

“That’s my baby. My first born,” she told WLS. “He always wanted to be a police officer because he always wanted to protect people. He wanted to make the world a better place.”

Mason’ body was escorted in a procession from the hospital to the Cook County Medical Examiner’s office with Chicago police, ISP and Chicago firefighters paying their respects.