The FBI executed a search warrant last month at Yahoo Inc. for information related to two e-mail addresses linked to the Craigslist postings, according to documents filed in U.S. District Court in Portland.
It is illegal to traffic in Native American remains. Kirk Francis, chief of the Penobscot Indian Nation, had reported the ads to state and federal officials and said he has reason to believe they were real.
The seller offered six scalps and related artifacts from a private family collection said to have been obtained by bounty hunters in the 1700s. Back then, bounties were offered for Penobscot Indians or for their scalps, Francis said. One proclamation, dated 1755, offered 50 pounds in British currency for every male Penobscot above the age of 12 and 40 pounds for their scalps.
If the scalps exist, Francis said they should be returned to the Penobscot reservation in Maine and given a proper burial.
"These are human beings that were murdered under genocidal policies, so we're concerned that in 2009 the effects of that policy are still here and there are still people who look at these pieces as nothing more than some kind of conquering piece of art," he said.
An FBI spokeswoman declined to comment, citing the agency's policy of not commenting on or confirming ongoing cases.
The ads, which are no longer accessible, ran twice in June, according to the FBI affidavit. The ads, which included a Maine cell phone number, said the scalps and other artifacts were part of a privately owned museum and were being sold because of a recent death among the owners.
A 1990 federal law makes it illegal for museums to have Native American remains and requires institutions to return remains to their rightful tribes, said Jason Brown, spokesman at Bar Harbor's Abbe Museum, which is devoted to Maine's Native American heritage.
Brown said he has never heard of people keeping scalps in private collections, but said it is hard to know exactly what is out there.
"Once they go into a private collection, it's hard to know unless they rear their head," he said.