Lawrence Phillips is dead at the age of 40, according to the California Department of Corrections and Rehabilitation.
Phillips was found dead in his cell early Wednesday at Kern Valley State Prison, where he was facing the possible death penalty in the alleged murder of his former cellmate.
According to Kern Valley State Prison, his death is being investigated as a suicide.
In 2008, Phillips was sentenced to 31 years in prison for convictions that included domestic violence, spousal abuse, false imprisonment and vehicle theft. In June, USA Today published a series of Phillips' harrowing letters from prison, many of which refer to the Nebraska program where he starred from 1993-95.
In April, 37-year-old Damian Soward was found unresponsive in the Kern Valley State Prison cell he shared with Phillips, who was immediately named a suspect in Soward's death. Per the Associated Press, officials later determined Soward had been strangled. Phillips was charged with first-degree murder.
Phillips was selected with the No. 6 overall pick of the 1996 draft by the St. Louis Rams but played just 35 NFL games with the Rams, Miami Dolphins and San Francisco 49ers.