Colt Brennan‘s cause of death has been determined four months after the athlete died in May.

The former University of Hawaii football star suffered an accidental overdose, caused by a lethal concoction of fentanyl, methamphetamine, amphetamine, and ethanol, a rep for the Orange County Sheriff’s Department tells PEOPLE.

Brennan, 37, died Monday, May 10, at Hoag Hospital in Newport, California, after he attempted to check into a detox facility, but was turned away due to a shortage of beds. Colt’s father Terry Brennan said his son was five months into a six-month rehabilitation program when he ingested something laced with fentanyl and lost consciousness.

“He went peacefully,” Terry told Honolulu Star-Advertiser, noting that Colt was surrounded by family at the time of his death. “He listened to Bob Marley. His sisters had a lei around him when he was unconscious. They had the music of Bob Marley playing near his ear.”

Colt became the starting quarterback for the Rainbow Warriors at University of Hawaii in 2005, where he set several NCAA records for college football, including second-most passing touchdowns in a single season with 58 (the record was later surpassed by Joe Burrow during the 2019 season). He was also a sixth place finalist for the Heisman Trophy in 2006, before coming in third place (behind Tim Tebow and Darren McFadden) in 2007.Colt Brennan wearing a blue uniform holding a ball © Mitchell Layton/Getty Colt Brennan

The Laguna Beach native was drafted to the now-Washington Football Team during the sixth round of the 2008 NFL Draft. Although he played during the preseason, injuries kept him from playing in regular season games, and Colt was later released in August 2010.

He had a brief one-month stint with the Oakland Raiders before he suffered a car accident in Hawaii in November 2010, which left him with a head injury, broken ribs, and a broken collar bone. Colt subsequently played for the United Football League, Canadian Football League, and Arena Football League, and he was last released from the Los Angeles Kiss in 2014.

Colt was arrested twice last year, once for causing a disturbance at a hotel while intoxicated, and again a few months later for another disturbance at his Hawaii home.

“It seemed to have an effect on him to where he just found himself going from one bad spot to another bad spot,” Terry told ESPN. “I don’t know how else to say it. You make decisions and sometimes they’re the right decisions, and sometimes they’re the wrong decisions.”

If you or someone you know is struggling with addiction, please contact the SAMHSA substance abuse helpline at 1-800-662-HELP.