'Death investigation' underway after trooper's shooting on the Dan Ryan

An Illinois State Police trooper has died after he was shot Friday afternoon on the Dan Ryan Expressway, with passersby coming to his aid and police driving him to the hospital.

Trooper Gerald Mason suffered a single gunshot wound.

Illinois State Police Director Brendan Kelly wouldn't give specifics about the shooting during a Friday evening news conference, saying it remains an ongoing investigation.

"This is a death investigation. We do not have any information that there is a cause for concern, that there is a threat to public safety, that there is a threat to law enforcement specifically," Kelly said.

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