Explorers Justin Fornal and Emiliano Ruprah may have solved the mystery behind the suspicious death of American explorer Captain Meriwether Lewis, who led the first American expedition across Western United States in 1804.

Lewis, along with his close friend Second Lieutenant William Clark, set out on the Corps of Discovery Expedition in 1804, commanded by the then President of the United States, Thomas Jefferson.

What was made out to be a scenic exploration on the outside was actually a top-secret mission. The duo had been sent out to find the strategic advantages for the Louisiana Purchase that Americans could use in case they needed to go to war on territories.

An illustration of explorers Lewis and Clark in the American frontier, 1931. Woodcut. (Photo by GraphicaArtis/Getty Images)

He is believed to have kept journals, maps, and letters that contained secretive details of the mission.

Murder or suicide?

October 11th, 1809, Meriwether Lewis died from gunshot wounds to the chest and head at Grinder's Stand, an inn on the Natchez Trace approximately seventy miles southwest of Nashville.

His aid, a man named James Neily is mentioned to have arrived 12 hours later at the scene to find him already dead. Most historians do believe that he had killed himself and had been behaving erratically because he had a type of syphilis.

However, a Masonic Apron was found on his person. DNA swabs were taken from that apron and two male DNAs were found on it - a groundbreaking find in the centuries-old mystery. A local newspaper also reported that his neck had been slashed.

Moreover, the multiple gunshot wounds beg the question - why would someone trying to kill themselves injure themselves instead of going for an efficient, painless kill? As it turns out, Lewis may have stumbled on a conspiracy that could have cost him his life.

Tennessee, Natchez Trace, Grinders Stand Replica Cabin where Meriwether Lewis was killed showing Interior and exhibits (Universal Images Group via Getty Images)

The Spanish players

The investigators find, through letters between the Spanish government and General James Wilkinson who was potentially a double agent, that Wilkinson had leaked information to the Spanish about the top-secret mission Lewis and Clark had been on.

The Spanish wanted their own claim to the territory of Louisiana and they could have sniffed the espionage, leading them to kill Lewis. Moreover, he had built a fort in the contested territory — Fort Clatsop in Oregon Country near the mouth of the Columbia River in 1805-1806, potentially declaring their ownership of the land.

However, the investigators find something more that leads them to believe there was another player.

A different empire

Lewis was appointed the Governor of the Louisiana territory in 1809. At the time, he could have uncovered a conspiracy involving then-Vice President Aaron Burr that could have had him assassinated.

In the letters between Wilkinson and the Spanish, the investigators find coded messages that mentioned Burr. They conclude that Burr had wanted to start an entirely different empire altogether, breaking away from the United States. A plan as big as that, if Lewis did stumble upon it, could have definitely got him killed.

Engraved portrait of Aaron Burr, the third vice president of the United States, an American politician from Newark, New Jersey, British America, 1790. From the New York Public Library. (Photo by Smith Collection/Gado/Getty Images)

They also find Neily mentioned in the letters, who was an aid to Lewis during his time after the expedition. He had been chosen and appointed by General Wilkinson!

In his letters, Neily mentions that he had in his possession Lewis' papers among other items. The day Lewis died, he had been off finding horses that had allegedly gone astray.

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