A man charged in the fatal shooting of two police officers during a traffic stop in Hattiesburg, Mississippi, was found unresponsive in his cell Friday night, officials said.

Marvin Banks, 29, was alone in an isolation cell when officers found him, the Forrest County Sheriff’s Office said in a statement. EMTs tried performing CPR before Banks was taken to the hospital where he was pronounced dead at 7:40 p.m. local time (8:40 p.m. ET), the sheriff’s office said.

Autopsy results showed Banks died of severe heart disease, but toxicology tests are still pending, Forrest County Coroner Butch Benedict said Saturday, according to NBC affiliate WDAM. Benedict said Banks’ body showed no signs of trauma.