Wild West outlaw Frank Stilwell (1856 – 1882) was born in Iowa, and ended up in Arizona in 1877. There, he had his first recorded run in with the law: he ordered coffee, but a new cook served him tea instead. So Stilwell shot him dead. As seen below, this wild man of the Old West was just getting started on a criminal career. It ended badly for him when he ran into the Earp brothers.
From Criminal to Lawman, and Back to Criminal

Frank Stilwell staked a claim and worked a mine in Mojave, Arizona, in 1879. When he got into a disagreement with a fellow miner over claim-jumping, Stilwell settled the dispute by grabbing a rock and smashing in his rival’s face until he was dead. He was arrested for murder, but the charges were dropped for lack of evidence. His violent track record did not prevent him from getting hired as a Cochise County sheriff’s deputy in 1881. He did not last long as a lawman, and was fired soon thereafter. It was not for police brutality or the like, though: Stilwell lost his job as a sheriff’s deputy because of “accounting irregularities”. From would-be crime buster, he pivoted back to crime.
A few months later, Stilwell robbed a stagecoach near Tombstone, Arizona. He was tracked down and arrested by lawmen Wyatt and Virgil Earp. Charges were dropped however for insufficient evidence, and after Stillwell produced alibi witnesses. It was the start of an antagonistic relationship that ended badly for Stilwell. The local charges against Stilwell for stagecoach robbery might have been dropped, but the Earp brothers were not about to let him get away that easy. In their capacity as US Marshalls, they charged Stilwell with the federal crime of with a mail carrier. That, however, created a perception that the Earps were persecuting Stilwell. It led not long after to the shooting and wounding of Virgil Earp, followed soon thereafter by the assassination of another brother, Morgan.
Frank Stilwell’s Dramatic End

Witnesses of Morgan Earp’s assassination stated that they saw Frank Stilwell flee the scene, and a Coroner’s jury listed him among the assassination’s suspects. Wyatt Earp then formed a posse and went after the suspects in the murder of his brother Morgan, and the earlier shooting of his other brother, Virgil. Two days after Morgan’s assassination, Wyatt Earp was tipped that Stilwell planned to murder his brother Virgil in Tucson, when the train carrying him and Morgan’s coffin to California stopped there. Wyatt formed an escort to accompany Virgil, and on March 20th, 1882, he spotted Stilwell and two associates waiting in ambush near Tucson’s train station.
Stilwell and his friends ran for their lives when they spotted Wyatt, but Stillwell stumbled. By the time he got back on his feet, Wyatt Earp was upon him. “I ran straight for Stilwell,” he later recounted. “It was he who killed my brother. What a coward he was. He couldn’t shoot when I came near him. He stood there helpless and trembling for his life. As I rushed upon him he put out his hands and clutched at my shotgun. I let go both barrels, and he tumbled down dead and mangled at my feet”. Stillwell’s bullet-riddled body was left besides the tracks near the Southern Pacific railroad depot, where it was found the next morning.

_________________
Some Sources & Further Reading
History Halls – What Made the ‘Wild West’ So Wild?
Southern Arizona Guide – Wyatt Earp and the Vendetta Ride
