The death of a man sharing a prison cell with former NFL running back Lawrence Phillips was ruled a homicide by strangulation, according to a coroner's report released Thursday.

Damion Soward, 37, was found lifeless early Saturday in a Central California prison cell, and he was later pronounced dead. The cause of death was neck compression asphyxia, the report by the Kern County Sheriff's Office said.

Officials have said they suspect Phillips, 39, an inmate at Kern Valley State Prison serving a sentence of 31 years and four months. It wasn't clear if Phillips has an attorney.

Once one of the nation's top college football players at Nebraska, Phillips played for the St. Louis Rams, until he was released in 1997 for insubordination. He also played for the Miami Dolphins and San Francisco 49ers.

He was convicted of twice choking his girlfriend in 2005 in San Diego and later that year of driving his car into three teens after a pickup football game in Los Angeles.

Soward was sentenced from San Bernardino County to serve 82 years to life for a first-degree murder conviction.