There seems to be some dispute as to whether Meriwether Lewis did or did not commit suicide. Many people involved in compiling evidence at the time believed he was murdered.
Early on, Lewis had some problems with the military, but charges were dismissed and he was promoted. After serving with the military, Lewis would eventually work for President Thomas Jefferson as "personal secretary and adviser for military affairs." eNotes.com sources state that Lewis was a very successful part of the Lewis and Clark Expedition. He was well-trained (by reading books from Jefferson's personal library and by Benjamin Rush) for the services that he, along with Clark, would provide as they "opened the trans-Mississippi region to American settlement." Returning from the expedition, Lewis was highly praised when arriving in Washington, D.C. eNotes.com also notes that he was psychologically distressed over financial problems and was "abusing alcohol and opiates." This same source notes that he took his life along the Natchez Trace, west of Nashville.
However, George Mason University's History News Network reports that there were a great many concerns regarding Lewis' death that made experts question the noted "cause of death" as suicide. In March of 2004, author Kathryn Moore, in The Mysterious Death of Meriwether Lewis, noted that debate regarding Lewis' cause of death has existed for almost two hundred years. Some time after his death "whispers" of depression and substance abuse traveled eastward, but a great deal of "ambiguity" existed regarding this information. There are many different versions of his death recorded at the time of his passing.
Some say he was shot twice, others say three times. Places mentioned are his forehead, back of the head, under his chin, in his sides, chest, abdomen, and back.
While many historians accept suicide as the cause of death, this is based on the word of James Neelly who traveled with Lewis as he headed east, but was not present at the scene of Lewis' death. Another thing that draws question to the actual cause of Lewis' death is Thomas Jefferson's selection of Lewis as his secretary and later as a member of the expedition. Would an intelligent man such as the President (who lived with Lewis for two years, while he was in Jefferson's employ) choose someone who was unstable for these tasks?
On the trip, Neelly and Lewis were separated. At a boarding house where Lewis (now a Territorial Governor in St. Louis) was staying, shots were fired, but the owner of the boarding house (alone as her husband was away) refused to open the door when Lewis was heard calling for water. She saw through cracks in the door that Lewis was crawling to get water from a bucket. One servant was said to have admitted to the act: "I have done the business." It is also said that "He complained that because he was so strong that it took him so long to die."
It is also noted that pistols then had very long barrels and it would have been nearly impossible for Lewis to have shot himself in the back of the head (which a later exhumation of the body showed). The absence of powder burns also raised serious questions. Some other reports noted that Lewis was found "lying by the Natchez Trace."
Depending upon who you choose to believe, Lewis may have died from depression and substance abuse. On the other hand, he may have been murdered, and it would be impossible to surmise the reason behind his death in this case.