If you're talking about Native American sites in the United States, you're probably thinking of NAGPRA--I think the Native American Grave Protection and Repatriation Act. Look up NAGPRA and you should be golden.
The Native American Grave Protection and Repatriation Act, or NAGPRA, was established in order to ensure that Native American artifacts, and specifically human remains, were treated with the proper respect. It came about after an incident in Iowa, when construction workers dug up over thirty human skeletons. Those of Caucasian people were quickly reinterred, but the Native American remains found were sent to a lab for study. NAGPRA also allows for artifacts to be given back to the tribe who lays claim to them, or repatriated. This part of NAGPRA applies especially to museums.
The Native American Graves Protection and Repatriation Act, or NAGPRA, is an act that protects Native American artifacts, especially human remains, from exploitative or inappropriate use, especially in museums or laboratories. The Act says that all institutions that receive federal funding must return all Native American remains back to the tribe holding claim on them. NAGPRA also dictates that if a museum or laboratory holds a particularly sacred or important item in its collection, the tribe has the right to ask for it to be returned to them, or repatriated. Under NAGPRA, tribes also have the right to visit museums and their storage to ensure that they are properly storing their artifacts and properly displaying them. If they disagree with a museum's treatment of a particular object, they may begin the repatriation process.
The group that put a quick end to the Kennewick Man study was a coalition of Native American tribes who claimed the remains under NAGPRA laws and requested their immediate reburial.
In the United States, the sale and purchase of human skeletal material is far less regulated than most people seem to believe. The only federal law regulating human bones is narrowly focused on native American bones and grave goods. This law is known as NAGPRA, the Native American Grave Protection and Repratriation Act of 1990. Otherwise, at this writing (May 2008) only two states have laws that restrict ownership and transfer of human skeletal material: Georgia and Tennessee. In all other states it is legal to purchase and own human skeletal material as long as it complies with NAGPRA. There are several internet vendors who import human skeletal material from Asia for sale. Vendor - Osta in Canada.In Canada unless you are becoming a doctor that requires this then beware! Students can get human skeletons and skulls alone, but often proof is needed as to why you need it. Some people donate their bodies to science and are called Cadavers. You can also go to specialty medical stores to buy this, but need proof as to why you need it.
On the side of repatriation and reburial. After such a bloody, abusive, genocidal history, the least we whites (including 'nonwhites' we've assimilated) can do is allow proper burial of the dead. NAGPRA is the law of the land. It was enacted in answer to long-held and previously-unheard concerns of Indian peoples. Many of these concerns are religious, involving the peace of ancestors, the peace of living descendants, and an all-important harmony with the land. Please, let us never insult these valid concerns. NAGPRA intended to adjust governmental and institutional policies to these concerns, and was very limited: to lands under some sort of federal control, to federally recognized tribes, and to human remains and funerary objects, excluding all other cultural objects, unrecognized tribes, and all other lands. The individual exhumed on a Kennewick riverbank controlled by Army Corps of Engineers meets all these strict requirements; other remains may deserve repatriation by rights, but this one by rights and by law. These remains have already been disturbed, photographed, studied, measured, poked, prodded, cracked, ground, X-rayed, analyzed, scanned, dissolved, spectrographed, dated, sampled, and displayed. While we acknowledge that none of this was done with malice, let us also admit that it was not done with awareness or sensitivity. Study, testing, critical thought, and the scientific method are valuable and helpful, but they are not the only game in town, do not benefit all equally, and do not cost all equally. And that's when they are applied to mere objects; let us eschew the chauvinism that fails to respect the views of remains as carriers of nonphysical realities. We have learned from this person, and some of the means of our learning are intrusive to the point of insult and anguish to those who are likely descendants. Enough already. Let us whites show gratitude, humility, and respect, be satisfied with the data we have from this, ask for no more, and put him to rest. Having said all that, it is also true that there are difficulties both scientific and cultural with linking remains to specific survivors, specific groups, specific tribes, and - as unamended NAGPRA requires - specific cultural practices. Which tribe should have the priviledge of hosting the services and reburial is not for eurodescendants or our institutions to decide; let them act together or send one representative, and decide without interference. Multiple tribes may all be correct in claiming ancestry. Scientists are probably correct in claiming that specific correlation over such a wide gap in time is imprecise and impossible to prove. Science and scientism can be as mistaken as any other -ism (if perhaps more ready to admit it than other -isms), and in particular may be hard-of-hearing when it comes to spiritual and religious concerns, connections with the Earth, and other traditions and practices outside their ken. Where a dominating culture still reaps the benefits and another culture still pays the cost of genocidal clashes, it behooves the benefitting culture to at least show some dignity for all survivors and more fully adapt dominant legal structures and actions. It really isn't much to ask for. Amidst so much uncertainty, let us not lose sight of the few certainties we do have: Kennewick man was not european, did not come from a scientific culture (nor a mercantile one, nor a materialist one), cannot defend himself against sacrilege, and is in a good position to be an ancestor of living modern peoples long abused who still care about the remains of their ancestors.