(NewsNation) — The family of Riley Strain, a University of Missouri student who went missing last month and was later found dead in a river in Nashville, Tennessee, are still demanding answers regarding his death. 

The family believes someone helped the 22-year-old into the river where his body was discovered weeks after he went missing. Strain’s family spoke with NewsNation senior national correspondent Brian Entin, saying they haven’t seen convincing evidence Strain fell in by accident.

Riley Strain’s family talked to NewsNation’s Brian Entin about Riley’s fraternity brothers, his messages about his drink and more in an extended exclusive interview. You can watch the full interview in the player above. Not sure how to watch NewsNation? Log in to this web player or go to JoinNN.com to locate us on your TV. 

Strain’s mother, Michelle Whiteid, claims his fraternity brothers partied while the family conducted a search. Whiteid said Strain’s frat brothers “all of a sudden disappeared” during the search and later showed up dressed to attend their formal that night.

Whiteid said on top of Strain’s friends choosing to party during the search, they apparently did not call 911 the night he went missing, either.

Stain communicated with his mom throughout the trip and texted her when they arrived at the hotel, she said. During the evening, Strain texted Whiteid saying he ordered a rum and Coke “that didn’t taste good.” Whiteid told Strain he probably shouldn’t drink it. He told her, “It tastes like barbecue.”

Strain disappeared March 8 during a trip to Nashville with his Delta Chi fraternity brothers. His body was discovered March 22 in the Cumberland River in West Nashville, Tennessee. Nashville police said the college student’s death appears “accidental,” with no trauma suggesting foul play, according to preliminary autopsy results.

Strain’s family has ordered a second autopsy that they hope brings clarity.

NewsNation’s Brian Entin, Katie Smith and Liz Jassin contributed to this report.