Investigators say Matthew Hall was found unresponsive in his cell at David L. Moss Tuesday.
Officers say Hall was found on the floor with a sheet tied around his neck.
Paramedics were able to resuscitate him and take him to the hospital.
Sgt. Craig Johnson was killed. Officer Aurash Zarkeshan is still in the hospital.
Hall is accused of driving David Ware away from a scene near 21st and Garnett last week after two officers were shot.