Three Northern California jail guards accused of beating to death a mentally ill inmate have also been charged with assaulting another prisoner.

Santa Clara County prosecutors allege in complaint filed Tuesday that the three assaulted inmate Juan Villa shortly before attacking 31-year-old Michael Tyree on Aug. 26.

Tyree was found dead in his cell around midnight Aug. 27. Investigators say Tyree died from internal bleeding and suffered significant liver and spleen damage.

Santa Clara County Sheriff Laurie Smith said last week that the three guards were the only people with access to Tyree's cell the night he died. Other inmates said they heard Tyree screaming in pain that night.

Guards Jereh Lubrin, Rafael Rodriguez and Matthew Farris appeared in court Tuesday, but they didn't enter a plea. They remain jailed without bail.