For 17 years, the fate of Jerry Michael “Mike” Williams remained a mystery.

The young father packed up his gear on Dec. 16, 2000, and drove out to Florida’s Lake Seminole to spend a few hours duck hunting on his boat. It was his last solo outing before he was supposed to go on a weekend anniversary trip with his wife, Denise.

The hours passed, and Mike never returned.

His father-in-law went looking for him and found his abandoned boat. His vehicle was still on the shore. But there was no sign of Mike.

But one person didn’t buy into the speculation. Mike’s mother, Cheryl, didn’t believe her son had accidentally drowned — and she pushed police to continue the investigation. After 17 years, police found a shocking explanation for what had happened to him.

The years-long mystery is featured tonight’s episode ofPeople Magazine Investigateson Investigation Discovery.

Titled “Mystery in the Swamp” the episode airs on tonight at 10 p.m. ET. (An exclusive clip is shown above.)

Courtesy Cheryl Williams

Mike and Denise Williams wedding photo.Credit: Courtesy Cheryl Williams

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During those 17 years, Cheryl stood on street corners with signs imploring police to solve the case and wrote more than 200 letters to the governor.

The results of her efforts — and the resulting police investigation — shocked all who knew Mike.

People Magazine Investigates: Mystery in the Swampairs tonight at 10 p.m. ET on Investigation Discovery.

source: people.com