A narrow lane off Highway 12 just outside Walla Walla, Wash., leads though pastures and creek bottoms to the Whitman Mission National Historic Site. The National Park Service runs this bucolic spread surrounded by the vineyards that let a dying farm town reinvent itself as wine country. A plush tasting room overlooks the historic area from less than a mile away.

The mission itself, in contrast, is a lonely, spooky landscape, and was nearly deserted on the overcast late autumn day when I visited. In fact, this is a murder scene: On Nov. 29, 1847, Marcus and Narcissa Whitman, who settled here to convert the Cayuse Indians to Protestant Christianity, died in a chaotic massacre, along with about a dozen others. The killers were mostly Cayuse men, but the event was more riot than uprising.

The "incident" led to war, executions and Oregon's political birth. Generations of Northwest kids have absorbed the story in history class. Today, the Park Service operates a small museum in a boxy 1950s building overshadowed by a lonely memorial obelisk. On June 4 of last year, the museum itself became the scene of a brand-new crime, vastly smaller in scale but resonant and, in a strange way, connected to Portland—a city recently recommitted to examining its own history through the massive Lewis & Clark bicentennial exhibit currently at the Oregon Historical Society.

Thieves paid the Whitman museum's $3 admission charge, then ducked into its one-room permanent exhibit, a sleepy chamber of native and settler bric-a-brac. They evidently had cased the target beforehand, and brought the specific wrench needed to dismantle the artifact display cases. Steady nerves, too, because they worked just beyond the museum desk's sightline. Only one thing disappeared: a footlong tomahawk with a 7-inch blade. Nine months later, the theft remains unsolved.

The tomahawk probably disappeared into the booming illicit trade in Indian artifacts. While other forms of culture crime—boosted Edvard Munch masterpieces or looted Iraqi museums—might draw more attention, the black market in Native American antiquities thrives despite massive deterrence efforts by tribes, museums and the feds. A variety of unsavory characters populate the business; Todd Swain, the National Park Service's leading antiquities-theft investigator, says cops often find looted native artifacts in methamphetamine labs. But if this were just any tomahawk, stealing it wouldn't be all that lucrative. Nineteenth-century trading companies mass-produced such quasi-ceremonial weapons and many tribes used them; you can get one on eBay for less than $300.

What recommended it to the thieves' attention? It is thought—or supposed—that this tomahawk was used in the massacre. Used, in other words, to crack open Marcus Whitman's skull.

Many, including some of the Cayuse tribe's own experts, doubt the weapon's connection. The museum itself presented the tomahawk without explanation. But if a buyer could be convinced of a grisly history, the tomahawk's underworld value would spike.

"The Whitman folks estimate it could go for, at the high end of the spectrum, $40,000," says Steve Yu, another NPS investigator. "Did it get stolen because it was a tomahawk, or because someone knows it's supposedly connected to the incident? It seems pretty clear that they knew what they were stealing."

As it happens, the missing tomahawk has a twin. On the third floor of Portland's Oregon Historical Society, another ax with murky but durable links to the Whitman killings hangs in a case alongside other mission artifacts. Though the description carefully reflects doubts about whether this is an actual murder weapon, the fact that the Portland tomahawk hangs just a few inches from a preserved lock of Narcissa Whitman's hair makes for an undeniable chill.

This winter's big-ticket show at OHS is the Lewis & Clark exhibit, a spectacular bonanza of original artifacts, interpretative films and sharp explanatory texts gathered by the Missouri Historical Society, making its only West Coast stop and closing this Saturday, March 11.

The show hammers home just how important physical artifacts are to our ability to grasp history. The time-stained rough draft of Thomas Jefferson's instructions to the explorers and the hollowed-out horn where Meriwether Lewis stashed his tobacco drag a well-worn tale out of the realm of myth into messy reality. The exhibit uses these raw materials to reinvent the expedition's dauntingly complicated backdrop of national, imperial and tribal politics.

And grand as it is, OHS's Lewis & Clark blockbuster is not complete without a visit to the permanent collection's tomahawk upstairs. Whether or not it was used to kill the Whitmans, the OHS tomahawk's link to its stolen twin shows how deeply entwined urbane Portland is with its wilder Northwest neighbors just a few hours inland. And the two tomahawks' saga proves that in the West, history is far from settled.

The Whitman killings were one of those incidents in which vast historical forces converged in mythic bloodshed.

The Cayuse became big players in Northwest tribal politics by acquiring the horse, just a few decades before Lewis and Clark came through. They were landlocked Vikings, raiding from the Willamette to the Rockies. By around 1810, they controlled a land empire straddling the future Oregon-Washington border. In their own context, they were ass-kickers.

Marcus and Narcissa Whitman were creatures of the cold war between the United States and Britain over "the Oregon Country" and intramural competition between Christian sects. In 1831, four Nez Perce traveled all the way to St. Louis to visit the Americans' chief Indian agent—none other than William Clark, explorer deluxe—to ask for "the white man's book of heaven." That sparked an evangelism boom among Yankee Protestants, also alarmed that Catholic "black robes" were spreading popery among the West's unsaved. The Whitmans, Methodists lacking neither piety nor ambition, interpreted a mandate to convert the Cayuse to Jesus and teach them how to farm.

But after 1842, their outpost's role as Oregon Trail way station eclipsed its religious function. The mission became a frontier version of Star Wars' Mos Eisley cantina: a magnet for shady characters and intrigue among Catholics, Methodists, tribesmen, Brits, Americans, traders and pioneers. Along with the new arrivals came new diseases, which devastated the Cayuse, by one estimate killing half the tribe by 1847. Whitman, a doctor by training, couldn't do a thing for his Indian patients; among the Cayuse, it was considered standard procedure to kill an unsuccessful medicine man. The massacre—never sanctioned by tribal leaders—also involved outsiders. One key instigator, for example, was a mixed-race wanderer named Joe Lewis who faded away after the killings, only to die (or so legend has it) in a stagecoach robbery near Missoula, Mont., years later.

The new white provisional government in the Willamette Valley didn't bother picking through the details. It raised a battalion of volunteers and marched them east. War unsettled the whole region for most of 1848. That August, the U.S. Congress, as alarmed by its distant colony's freelance military venture as by the massacre itself, created the Oregon Territory to put D.C. firmly in charge. The newly appointed governor demanded that the Cayuse turn over the massacre's perpetrators. Promptly convicted, five Cayuse men were publicly hanged in Oregon City on June 3, 1850.

The daring theft at the Walla Walla museum prompted Richard Engeman, the OHS public historian, to review the history of the Portland tomahawk. The society acquired the weapon in 1899, shortly after its founding, and long made it a highlight of various exhibits. Records confidently state that the weapon is "fully documented."

"But that's all it says," Engeman says. "Thanks for the help. When you look at the item, it looks more ceremonial than like a weapon of destruction. You wonder. The trail of ownership should say, 'We acquired this from so-and-so, who got it from so-and-so,' all the way back to the scene. There should be a connecting story line. We don't have one. And if it doesn't have that story behind it, it's a different object."

Engeman grew up near Astoria, learning the Whitman saga as a primary Oregon creation myth. He's watched the story's interpretation change dramatically over time. Today, the tomahawk is presented in a completely different way than it once was, as one small piece of a highly nuanced tale.

"When I was a child, there was this idea that Whitman 'saved Oregon' for America," says Engeman. "Now, this exhibit is about religion, and native inhabitants. Those things once weren't a big deal."

And in a few decades or even a few years, it's certain that the tale will shift again. For one thing, the Cayuse haven't had their last word. As one of the Confederated Tribes of the Umatilla, they're part of a political ecosystem in which tribes—thanks to gambling money—are suddenly on the rise. Portland, meanwhile, is filling with fresh blood and moving deeper into the global economy. But to keep its soul, the city must keep one foot firmly planted in the old Oregon Country and its dark and bloody history. The disappearance of any part of that past is a minor tragedy in the sad but fascinating epic that produced everything around us.

"Was this tomahawk a Picasso?" asks Swain, the National Park Service investigator. "No. But nothing becomes part of a national park unless Congress and the president decide that it's vital to the country's heritage. Maybe not a lot of people came to the Whitman museum, but I would argue this is a significant theft. Should this stuff be accessible to the public at all—do we just make a replica? But if you do that, the experience is diminished. There's something just super-cool about seeing the real thing, but this is the risk that's involved."

See the Portland tomahawk for yourself at the Oregon Historical Society, 1200 SW Park Ave., 222.1741. 9 am-9 pm daily.

Lewis & Clark: The National Bicentennial Exhibition

at OHS runs through Saturday, March 11. $15 adults, $13 students and seniors.