Ex-NFL running back Lawrence Phillips has been charged with first-degree murder in the strangulation death of his cellmate at a California prison.

Phillips, already serving a sentence of more than three decades behind bars, allegedly killed Damion Soward, 37, at Kern Valley State Prison in April.

Phillips, 40, will not face the death penalty if convicted, according to USA Today.

A college star at Nebraska, Phillips finished eighth in Heisman voting during his sophomore year in 1994.

He was selected sixth overall in the 1996 NFL draft by St. Louis. Phillips played three seasons with the Rams, Miami Dolphins and San Francisco 49ers, scoring 14 rushing touchdowns and one receiving touchdown. His best game came in the 1997 season opener as the Rams beat the Saints, 38-24. Phillips ran for 125 yards and three touchdowns, both numbers setting career highs he would not match.

Phillips is serving a sentence of more than 31 years after he was convicted of choking his girlfriend and later driving his car into three teens after a pickup football game. He's due back in court to face the murder charge on Sept. 15, KBAK-TV reported.

The Associated Press contributed to this report.