CHICAGO (CBS) — The death of an Illinois State Police trooper who was found in his cruiser with a gunshot wound on the Dan Ryan Expressway has been ruled a suicide.

The Cook County Medical Examiner’s office made the ruling Saturday for Trooper Gerald Mason’s death Friday afternoon. Mason, 36, was an 11-year veteran of the Illinois State Police.

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On Friday afternoon, red and yellow police tape was stretched across the inbound lanes of the Dan Ryan (I-90/I-94), after the trooper was found in his SUV near 43rd Street. A passerby saw that trooper inside his car. That’s when she ran over to him and had to use the trooper’s car radio to call for help.

Witnesses told CBS 2’s Asal Rezaei they saw people frantically running over to the trooper’s vehicle. Moments later, police arrived, and witnesses saw officers place him in an unmarked police car and speed to the hospital.

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Sources said the trooper was taken to University of Chicago Medical Center in critical condition. The Cook County Medical Examiner’s office confirmed the trooper later was pronounced dead.

The trooper’s mother, Linda Mason, said her son always wanted to be an officer.

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“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,” said Director Brendan Kelly.

CBS 2 Chicago Staff