Actually, he was beaten (per Wikipedia article):
"He was severely beaten by several guards, secured in a straitjacket, and confined to a darkened cell." "He died after two weeks, on August 13, 1865, aged 47, from a gangrenous wound, due to an infection on his right hand which might have been caused by the struggle. The autopsy gave the cause of death as pyemia—blood poisoning.[64]"