Chip Colwell, senior curator of anthropology at the Denver Museum of Nature and Science and author of "Plundered Skulls and Stolen Spirits."

(Michael Sakas/CPR News)

Who owns the past? That question is at the heart of  a 1991 law that requires museums to return Native American artifacts to tribes.  The items, collected by museums over centuries, often include spiritual objects and human remains.

The law has also reshaped the role of the Denver Museum of Nature and Science and its senior curator Chip Colwell. The Denver museum began returning some Native American artifacts even before the 1991 Native American Graves Protection and Repatriation Act required it. In the last 10 years, it has returned almost all the Native American human remains in its collection to tribes that requested them. Colwell's new book "Plundered Skulls and Stolen Spirits," is his personal account of working with the law and the native people it impacts.