Former Rams running back Lawrence Phillips died early Wednesday in what California prison officials deemed a likely suicide.
Phillips, 40, was found unconscious just after midnight during a security check by staff at Kern Valley State Prison in Delano outside Bakersfield, the state corrections department said in a statement. He was taken to a hospital where he was pronounced dead more than an hour later.
Phillips had been held in the prison's administrative segregation unit since April.
Last year, Phillips allegedly killed his cellmate at Kern Valley. His trial in that killing was in its early stages in Kern County, officials said.
Phillips was serving a 31-year sentence after he was convicted of domestic violence, false imprisonment and vehicle theft.
Phillips was a standout at the University of Nebraska who helped the Cornhuskers win two national championships, but he was cut from several NFL and Canadian Football League teams for a range of disciplinary problems.
He played with the St. Louis Rams and the San Francisco 49ers, among other teams.
He was arrested at least five times on suspicion of assaulting women, and he was convicted in 2006 of driving a Honda Accord onto a field near the Los Angeles Coliseum and striking three teenagers.