Great Lakes Fire Department Lieutenant Jeff Peters. | Provided Photo

The medical examiner said the sudden death of an off-duty Great Lakes Fire Department firefighter, who leaves behind three children, has been ruled a suicide.

The Great Lakes Fire Department, based near North Chicago, announced the death of Lieutenant Jeffrey Peters on Sunday. “We are devastated by the loss of one of our own.”

Chicago police officers found Peters in his vehicle in the 2300 block of West Diversey Avenue in Chicago around 11:30 p.m. Saturday. Paramedics pronounced him dead at the scene.

The Cook County Medical Examiner’s Office conducted an autopsy on Sunday and said Peters’ cause of death was a gunshot wound. They ruled his death a suicide.

The Great Lakes Fire Department covers the Naval Station Great Lakes in Lake County and is one of the busiest fire departments in the U.S. Navy.

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Peters was an “integral part” of the Great Lakes Fire Department for 21 years.

Peters responded to countless structural, medical and rescue calls as well as calls for mutual aid from fire departments in the region, “saving lives and property, and providing hope to the people in our charge in their darkest hours,” the department said.

“Jeff was an outstanding firefighter, friend, and mentor. He was a colleague we always looked forward to having on shift and a colleague we were always grateful to have on scene, no matter the call.”

Peters, who resided in Kenosha, Wisconsin, was assigned to Tower 1931.

The intelligence, friendship, and dedication Peters brought to the department “will be sorely missed,” the department said, adding that “Great Lakes has a hole in its heart today.”

“The sudden loss of a true and trusted colleague and friend reminds us to cherish our brothers and sisters, and we hold on to the hope that brighter days lie ahead,” the department added.

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Officials asked the public to keep Peters’ family, particularly his three children, in their thoughts and prayers.

A GoFundMe fundraiser was created by co-worker Christopher Dowdall on behalf of Peters’ family.

“[His children] were, and will always be, his proudest accomplishment and today we rally around them,” Dowdall said.

“Every penny raised through this effort will go towards financially supporting Jeff’s family. We also realize that in times such as these donations may be hard, however, a share, a like, or support is just as valuable, if not more.