I read a little about it after seeing this post. If I read it right he admitted to taking part in a gun battle in which the two FBI agents were killed but that he himself didn't execute them?
Incidentally my dad grew up in Bennett County, SD which is right next to the Pine Ridge reservation. He said some of the Sioux kids would come to HS unable to speak English as they only spoke the Sioux language at home. We've visited up there several times. The PineRidge reservation is the poorest part of the US I've ever seen, poorer than any inner city I'm familiar with. It's definitely not like OK.