The FBI is joining the probe into the death of a man who was allegedly left naked on a concrete jail floor for days until he was transported “limp” and “not alert and conscious” to an Alabama hospital. Within three days of his stay at the Walker County Jail, Mitchell had been shocked with a stun gun, which caused his false teeth to fall out of his mouth, the suit alleges, also citing video a corrections officer provided. The emergency room doctor described being unaware of the underlying cause of Mitchell’s hypothermia but believed it “was the ultimate cause of his death,” the document says