"All we're looking for is the truth," said relative Howell Lewis Bowen. "The family is united in trying to resolve the mystery."
In 1809, Lewis was found dying of multiple gunshot wounds in a tavern where he had stopped for the night about 70 miles from Nashville, Tenn., on the Natchez Trace.
Some historians believe he killed himself. Others believe he was assassinated, possibly by political enemies. At the time of his death, Lewis was serving as governor of the Louisiana Territory under President Thomas Jefferson.
The National Park Service, which owns the land where Lewis is buried in Hohenwald, Tenn., has refused requests to exhume his body, the Charlottesville (Va.) Daily Press reported Friday.
Bowen, and other family members, have established a Web site -- SolveTheMystery.org -- to gather support for their effort to exhume Lewis, best known as the leader of the 1803-1806 Lewis and Clark Expedition to the Pacific Coast.
National Park Service officials were not available for comment, the Daily Press said.