(NewsNation) — Two weeks since searchers found the body of Riley Strain in the Cumberland River near Nashville, his family is still looking for answers — and for some people to step up.

“We haven’t really heard much from them,” Riley’s father, Ryan Gilbert, says of his son’s fraternity brothers. “There’s a lot of things we’d like to find out from them.”

The University of Missouri student was in Nashville to party with fraternity brothers, but left them when he was ejected from a bar.

“If I was in their situation, I’d be beating down those parents’ doors to tell them everything I could and be helpful in any way that I could,” Gilbert said.

That shocks private investigator Steve Fischer, who’s been working with the family.

“This family needs peace of mind … to know if this is an accident or if something else happened. I would think everybody would be coming forward.”

Fischer also tells NewsNation’s “Elizabeth Vargas Reports” he’s hit roadblocks in his search for more surveillance video from cameras along Strain’s route to the river.

“I would like to know where the camera footage (is) from the county building that’s just past the bridge. That building has multiple cameras on it.”

But he says it’s been difficult getting cooperation from the police and from some businesses.

“I also tried to get footage from the Marathon (oil) facility right across the river. (But) once I notified law enforcement, I was kinda shut (out) of the process.”

As Fischer pursues video and other people who might have encountered Riley in March, Gilbert says the family is still waiting for toxicology test results from Strain’s body. But he says that could take another two to three months.