Blair County Deputy District Attorney Wade Kagarise tells the Altoona Mirror 62-year-old Aaron Dishong died early Friday.
Warden Michael Johnston did not immediately return a request for comment.
Dishong was ordered Wednesday to stand trial for the Nov. 15 blaze that killed 3-year-old Darrel Etchison Jr. in Altoona. The boy's mother and little sister escaped the blaze.
Investigators say Dishong was irate an ex-girlfriend he believed was in the house was dating a black man. Authorities say the woman had left the night before.
A neighbor testified Dishong told her he'd set the fire, but police recorded a call in which Dishong said he hired a Ku Klux Klansman to do it.
