A collosal injustice, even if you don't think killing two FBI agents was justified.
(Apologies if I over simplify, buts it's been a long long time since I read about this and am going off memory)
The extradition and a decent chunk of thr trial was a fucking sham, full of false confessions and fake statements that the court pulled nonsensical shit to make stick (eg a 'witness' statement was deemed accurate and reliable, but the witness who gave it claimed they were coerced and did not say that, but their claims were not allowed to be heard because thr court said they were 'mentally unfit' only when disputing the false confession).
And anyone who's given the details of the shootout ever a cursory read knows the FBI story is bullshit and it was almost certainly self-defense. The two agents killed lied about the vehicle description, lied about who they were following, lied about who shot first on the radio calling for backup and had pulled up on Peltier and the others in the truck, on private property, in two separate unmarked cars, seemingly because of his position in AIM and because he'd refused to help hand over Jimmy Eagle the previous day. They were out for payback.
And keep in mind they wanted Jimmy Eagle primarily for the high crime of a supposed theft of a pair of cowboy boots from local ranchers who already had issues with the indigenous communities.
Bullshit from top to bottom.
Still, he's alive and they aren't, which clearly wasn't their plan.