The FBI is investigating the theft of a ceremonial tomahawk believed to be the weapon used to kill Dr. Marcus Whitman, the 19th century missionary and one of the leaders of Northwest settlement. Whitman and his wife, Narcissa, were killed on Nov. 29, 1847, by Cayuse warriors who blamed the Whitmans for a deadly measles epidemic.

The tomahawk disappeared from a display case during visiting hours at the Whitman Mission National Historic Site in southeastern Washington. The thief used a special tool to dismantle the case, said Roger Trick, chief of interpretation at the site.

"Someone brought in exactly the right-sized wrench," Trick said.

Steve Yu, a criminal investigator for the National Park Service, said there were no leads or suspects.

"It might be solved in a year; it might not show up for 20 years," Yu said.

The hatchet-like weapon is one of two so-called "Whitman tomahawks" that may have been used to deliver the fatal blow. The second is on display at the Oregon Historical Society in Portland, Ore., where officials are careful to note there is no way to be sure if either one was actually used nearly 160 years ago.

Both tomahawks were fashioned of iron with hollow wooden handles and designed for dual use as hatchet-style weapons and ceremonial tobacco pipes.

Five Cayuse men were charged with killing 14 of 72 people at the Whitman Mission at Waiilatpu, "the place of rye grass," just west of Walla Walla.

Whitman, 45, was killed with a tomahawk but his wife, Narcissa, 38, died of gunshot wounds suffered in the attack.