Marvin Banks, who was being held in the deaths of two Hattiesburg police officers, was pronounced dead Friday night at Forrest General Hospital.
Forrest County coroner Butch Benedict confirmed Banks, 29, of Hattiesburg, was found unresponsive in his cell at the Forrest County Jail and taken to Forrest General, where he was pronounced dead after 8 p.m. Friday.
Benedict said an autopsy was planned for Saturday at the state crime lab in Jackson.
"Everything is still an ongoing investigation," Benedict said.
Forrest County Sheriff Billy McGee said CPR was performed on Banks before he was sent to the hospital.
Banks had been arrested hours after Hattiesburg officers Benjamin J. Deen and Liquori Tate were shot to death the night of May 9 near East Fourth and Bouie streets, close to downtown Hattiesburg.
He was charged with two counts of capital murder, as well as possession of a firearm by a felon and grand larceny for taking one of the officers' cruisers and fleeing.
Nine people were arrested in connection with the deaths of Deen and Tate.
The Mississippi Bureau of Investigation will handle the investigation into Banks' death.