The Communists have a long history of using minorities and people with grudges for their own purposes. They played on nationalist resentments against colonialism all over the third world. They played on black resentment against America (e.g. Paul Robison). They played on Indian resentment against Hispanic rulers in South America. The hatred and resentment of other people are useful tools for them.
Muslim terrorists obviously see the same opportunities--to convert black criminals in prison, for instance, or to ally themselves with the Basques in Spain.
So filiations among Communist radicals, Muslim terrorists, and AIM would be all too natural. Real Indians with a sense of pride in themselves might not fall for this stuff, but marginal and resentful Indians who blame the white man for all their troubles very well might.
The only point you suggest that I find hard to believe is that they would kill this little girl because of the coincidence of a name. I'd look for some other connection, maybe, between the parents and AIM or other Indians. How much does an unsolved murder case really hurt the FBI? What AIM needs is more along the lines of another Ruby Ridge, some means of stirring up hatred between the FBI and the Indians, and this really doesn't do it.
Look, I think the killer was mainly motivated by his mental illness--not his radical affiiliations.
But he needed some sort of ideological justification for his sick perversions.
He is someone who cannot accept that he is a violent killer, so he gives himself a veneer of "respectability" because of his radical politics.
The signatures make his crime, in his mind anyway, justifiable as an act against the government, FBI, police and John Ramsey.
The kind of people who belong to AIM like to hate others.They are into violence. A lot of the AIM people were into drugs.
The ideology makes this murder OK, heroic even.
By leaving the signatures --the attack on John Ramsey's most precious possession, the SBTC, and possibly the cowboy boots, he is validating that this is a political act. Of course it isn't.
Then look at how Peltier's lawyer Lee Hill tried to manipulate the evidence and be close to the investigation afterwards. He was a source of all kinds of conspiracy theories. He subsequently was arrested twice and now disappeared.
He even had little filed knives which I think are to open locks.