A year ago this month, Keylan Knapp, a student at the University of Wisconsin-Milwaukee, disappeared from his home. His mom and dad immediately became worried, as their 20-year-old son had been diagnosed with anxiety disorder at around age 11 and had stopped talking a few days before he disappeared.

“I went over with him the night before, and he wasn’t feeling well. I gave him two large bottles of Nyquil for the night,” Richard Knapp, Keylan’s father, told CBS News. “We called 911. We did everything we could for him.”

On March 30, 2018, Keylan left his home, by himself, to walk two miles to a gas station. But once inside, he did not come back. That’s when his worried parents filed a missing person’s report. Keylan was described as 6 feet 2 inches tall, weighing about 180 pounds, with black hair and blue eyes. The missing student was last seen wearing a purple T-shirt, blue jeans, and work boots.

After Keylan was reported missing, a massive search was organized by the Wisconsin Department of Justice to find Keylan. Law enforcement from 16 different departments had been dispatched to the area as the search continued for weeks. The Dane County Sheriff’s Office, Madison Police Department, and Wisconsin State Patrol teamed together to carry out the search. “I could hear his voice, telling me, ‘Dad, they’re looking for me, daddy. They found my last cellphone in the middle of the woods,’” Richard said. “So he was telling me things that really upset me.”

At that point, police searched a dump in the area, but they did not find anything. Detectives searched the area around campus and nearby surrounding neighborhoods, but there was no indication of where the missing student had gone. The search continued through April and an Amber Alert was put out by the Dane County Sheriff’s Office.

“It’s very emotional knowing that I don’t have him,” Richard said. “I don’t know what happened.”

At the time, Richard and Keylan’s mother thanked the law enforcement officials who participated in the search for their help.

“I personally appreciate how diligent and devoted you guys are to the public. You do a great job,” Richard said. “From the bottom of my heart, I’m sorry this happened to our family.”

In the weeks after Keylan’s disappearance, various theories emerged about his disappearance. One theory, the motive, was given on a podcast by one of Keylan’s professors. The theory, which was disputed, was that Keylan had been killed by someone who was “caught” doing something that Keylan had ended up saving.

Keylan’s parents were in shock when they heard about this theory. “What they heard was a completely unheard of, monstrous event. We never felt that way. But I was in shock. And I don’t have words to say how I felt about that,” Richard said. “Someone was not afraid to kill Keylan. It took that behavior to be able to move on with that murder.”

Keylan’s parents have filed a lawsuit in Dane County Circuit Court against the town of Greenwood. The suit claims that someone murdered Keylan in the neighboring town of Greenwood. “His body was dumped in the woods in town of Greenwood, which is a tiny town and everyone knows everyone,” Richard told CBS News. “They know who did it.” The lawsuit seeks damages for the loss of their son, citing the town’s alleged negligence.

Keylan’s parents maintain that they still hold out hope that he will be found alive. However, Richard’s view of his son has changed dramatically.

“He was a sweet boy,” he said. “He was a really tough-as-nails kid. He was a fighter and when he had a bad day or when things got really tough, he would come back, and he would pull through. So I think at first, we had the same perspective, and then after two weeks, we had changed.”

Read the full story at CBS News.

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