SOLEDAD, Calif. (AP) — A prisoner at a central California lockup died after he was attacked by two other inmates, authorities said Friday.

Oracio Ramirez, 30, who was serving time for first-degree murder, was attacked Thursday morning in a recreational yard at Salinas Valley State Prison.

A guard fired a less-than-lethal device that stopped the attack and an ambulance was called while staff performed life-saving measures. But Ramirez was pronounced dead about 20 minutes after the attack, authorities said.

A weapon made by an inmate was found at the scene and Ramirez’s death is being investigated as a homicide, authorities said.

Two prisoners have been placed in restricted housing while the investigation continues, corrections officials said.

Ramirez was sent to prison in 2014 from Tulare County to serve a sentence of life in prison with the possibility of parole. He was convicted of first-degree murder, robbery and criminal gang activity, authorities said.

Earlier this year, while behind bars, he was given another sentence of nine years for an attempted murder, corrections officials said.