Unlikely. I can’t think of any immediate reasons that federal courts would consider anything different to the states, where something so heinous as rape of a child is concerned.
I think it’s not about his freedom, but one of the two courts that could charge him have the death penalty. His legal case is about avoiding that.
He was already convicted and sentenced to 1,000 years. So I don't think the death penalty was on the table.
What would the tribal law sentence be for the same crime?