Lawrence Phillips has been accused of killing his cellmate at Kern Valley State Prison in California, where the former NFL running back is serving a 31-year sentence for several charges stemming from 2005, according to the Los Angeles Times. Damion Soward, 37, who was sharing a cell with Phillips and was serving an 82-year sentence for murder, was found unresponsive in his cell on Saturday.

Phillips, 39, was found guilty in 2005 in two separate criminal cases, one involving choking his girlfriend twice in San Diego and one related to him striking three teenagers with his car after driving onto a field in Los Angeles. A jury sentenced Phillips to 31 years in prison in 2008.

Phillips was one of the most promising running backs in college football of his time and was a standout during his three years playing for the University of Nebraska Cornhuskers in the mid-1990s. But his off-field troubles had already begun.

Prior to his 2005 conviction, Phillips was arrested at least five times for assault. In 1995, Phillips was temporarily suspended from playing for the Cornhuskers after he was charged with assaulting his former girlfriend. He was later allowed to play the season’s final four games. He went on to play for the St. Louis Rams and San Francisco 49ers, among other teams.

Officials were investigating Soward’s death. It was unclear whether Phillips had an attorney, according to ESPN