I found this hilarious, at least at first. The courts can't reject the Umatilla tribe's claim of connection to the Kennewick man, because that would be rejecting their religious beliefs? Hilarious.
According to NAGPRA, if human remains are found on federal lands and their cultural affiliation to a Native American tribe can be established, the affiliated tribe can claim them. The Umatilla tribe of Native Americans requested custody of the remains, wanting to bury them according to tribal tradition. However, their claim was contested by researchers hoping to study the remains; if Kennewick Man has no direct connection to any modern-day native tribe, then NAGPRA should not apply.
The Umatilla argued that their creation myths say that their people have been present on their historical territory since the dawn of time, so a government holding that Kennewick Man is not Native American is tantamount to the government's rejection of their religious beliefs.
So what happens if I believe, as part of my religion, that Native Americans, in ancient times, defected from and killed off a righteous civilization? What if I believed--religiously, of course--that Native Americans deserved retribution for this crime? You can't say that they did nothing to deserve it, because that would be tantamount to rejecting my religious beliefs!
If you thought I was just making that religion up, you'd be wrong. This has historically been believed by Mormons.
After reading that, I looked around Wikipedia some more (you know how it is), and I read about the American Indian Religious Freedom Act. I have somewhat mixed feelings about this. I'm all for religious freedom, but under most circumstances, religious people should not be allowed to do things that would otherwise be illegal. I consider the AIRF act to be a sort of grandfathering in of Native American religions. If a group started a new religion and just claimed that, say, marijuana was part of their religious practices, then I doubt that this would be legal, because this new religion has not been grandfathered in.