So which was it, murder or suicide?

Just as scholars can't agree on just where the Lewis and Clark Expedition began -- Pittsburgh? St. Louis? Charlottesville, Va.? -- a debate also rages over how explorer Meriwether Lewis reached his final resting place.

For nearly 200 years, controversy about Lewis' death -- at age 35, in a small log cabin in the Tennessee mountains, just three years after concluding his triumphant expedition to the Pacific with William Clark -- has simmered, bubbled and occasionally boiled over.

Today, a group of his descendants will be trying to turn up the heat again at a news conference in Washington, D.C, as part of a so-far-unsuccessful effort to persuade the National Park Service to exhume Lewis' body so scientists can render a verdict on the cause of death.

"We don't care how he died, we just want the truth on how he died," said Howell Lewis Bowen, 73, the explorer's great-great-great-great nephew. He, along with dozens of other "collateral" descendants of Lewis' sister Jane -- the explorer had no children -- has been fighting since 1996 for federal permission to exhume his remains, to no avail.

Lewis is buried on the Natchez Trace Parkway in Tennessee, a 400-mile-long wilderness trail that also is federally protected land. While a coroner's jury in Tennessee ruled in 1996 that his body should be exhumed, the park service denied a subsequent permit application to do so because of a policy "that we don't disturb the graves of those who are buried in national parks," said Bill Reynolds, a spokesman for the agency's regional office in Atlanta.

That hasn't deterred Mr. Bowen or other relatives, like Thomas McSwain, of Shepherdstown, W. Va., from pressing their case. With the support of nearly 200 Lewis descendents, they resubmitted their application to the park service earlier this year, seeking an exhumation, a scientific study and a proper Christian reburial of Lewis's remains.

Actually, this wouldn't be the first time Lewis' body was dug up. In 1848, when the monument for his grave was erected, his bones were positively identified by the man who built his coffin -- recognizing its specially manufactured iron nails -- and a monument committee reported to the Tennessee legislature that it "was more probable that he died at the hands of an assassin."

More recently, many historians -- most notably the late Stephen Ambrose in his book "Undaunted Courage" -- argued that the explorer was depressed and ultimately took his own life after repeated suicide attempts.

Mr. McSwain, a great-great-great-great nephew of Lewis, argued that historical evidence was purely circumstantial, and that the sole witness gave differing accounts of what happened at Grinder's Stand, an inn where most scholars believe Lewis shot himself on Oct. 11, 1809.

But not all scholars. "There's a theory that he had a resurgence of malaria, which he'd contracted earlier in life, or that he was murdered in a robbery or assassinated for political reasons," Mr. McSwain said. "What happened is anyone's guess, and the family's position is that we need to find the truth."

The park service's resistance is said to be based on a fear of a run on exhumations at national monuments around the country. And indeed, there's been something of a boom market in such post-mortem detective work: James Starrs, a George Washington University professor and forensic expert who has led the effort to study Lewis' remains, was involved in a similar project involving Jesse James, while others have been busy analyzing Beethoven's hair for signs of syphilis.

Dr. Starrs rejected what he called "the sanctity of the grave argument" in a phone interview yesterday, noting that there is precedent for other exhumations at other park service sites.

"We've been working on this for more than 10 years and they've laid roadblocks all the way down the line, although there is no evidence this will open the floodgates to anything."

In 2008, the park service's resistance appeared to weaken when, after an independent review was conducted, Lyle Laverty, assistant secretary of the Interior for Fish and Wildlife and Parks, wrote to the family's lawyers, declaring the proposed exhumation to be in the public interest.

Earlier this year, though, some family members received word that the park service would probably deny their application again -- so they hired a public relations firm and set up a Web site, www.solvethemystery.org to focus public awareness on the issue.

"The family has been relatively quiet up until now, but now they've decided they need to speak out," said John Egan, a representative of Elizabeth Christian & Associates, a public relations firm working on the Meriwether Lewis exhumation project on a pro bono basis.

While the permit process for exhumation is moving forward, there are many bureaucratic hurdles ahead, Mr. Reynolds noted -- most notably the National Environmental Policy Act, which requires an environmental assessment, to be paid for by the family, and opportunities for adequate input by the public and historic preservation officials in Tennessee.

."We want to get information and input from all the family members who are descended from Meriwether Lewis," Mr. Reynolds said. "We have a process we're required to follow by law, and we'll continue to follow that process."

That's fine with Mr. Starrs, who notes that all but one of Lewis' descendants has signed a letter supporting the exhumation -- and that lone holdout nonetheless provided him with a DNA sample to use in the subsequent forensic investigation.

"That's pretty interesting, isn't it?" he said. "She wants to make sure that we get it right, even though she's not signed on. The bottom line, though, is that all the other descendants want it done, and that's a pretty solid argument."