Father of missing college student Mollie Tibbetts believes she's with someone she "trusted"

BROOKLYN, Iowa — The father of missing Iowa college student Mollie Tibbetts says he believes his daughter may have left willingly with someone she knew. Tibbetts, 20, was last seen taking her daily jog nearly three weeks ago.

"I think someone went to the house that Mollie knew or that Mollie trusted and that she left with them willingly," Robert Tibbetts told CBS News correspondent Adriana Diaz. "Now they're in over their head and they don't know what to do."

Tibbetts' family describes her as a light, who loves to lift others. Her personality is on display in a 2016 video, where she's seen addressing her peers at a faith event.

"Everyone has their own talent, whether it's a sport you're good at or if you're good at dance or if you're a great writer, or even if you're just a good person -- that's one of the best things you can be good at," she says.  

Tibbetts' parents got a call on Sunday that they'd been dreading. Investigators found a body, but they couldn't confirm that it was their daughter.

Missing Student

This undated photo released by the Iowa Department of Criminal Investigation shows Mollie Tibbetts.

Iowa Department of Criminal Investigation via AP

"The FBI agent called us and she told me I don't want you to hear this on the news," said Laura Calderwood, Mollie Tibbetts' mother.

Investigators soon announced the body was not Tibbetts, but of 20-year-old Sadie Alvarado who was found on the side of a road in Lee County, Iowa.

"We immediately, when we found out, thought about that family and the tragedy that they went through, and this in no way diminishes their pain," said Robert Tibbetts.

Wayne Cheney, who lives near the search area, says he's been questioned by the FBI at least five times about Tibbetts. The former hog farmer has several convictions including stalking and harassment, and charges in seven other cases have been dismissed.

He told Diaz someone from the FBI wanted him to take a polygraph test.

"I said 'No, I'm not doing it,'" he said.

Tibbetts is one of more than 88,000 active missing persons cases in the U.S. Her search continues to make national headlines. Brooklyn, Iowa is plastered with her face, which is even on billboards outside the state. The outpouring of support has touched Tibbetts' parents.

"I think it's because people see in Mollie their own daughters, their own girlfriend, their own sister," Robert Tibbetts said.

"I think it struck a chord with people that, you know, this could be happening to me right now, to my family," Calderwood said.

Mollie is more than Robert Tibbetts' daughter. At his wedding earlier this year, she was his best man. He says if he could talk to his daughter, he would tell her to "hang on."

"We're gonna come get you," he said. "Everybody's looking."

Police have still not identified any suspects or made any arrests in the case. CBS News spoke with Tibbetts' boyfriend, who says he's also been questioned by investigators but is not a suspect. A reward for information about the case is now more than $277,000.