Charles H. Moyer, president of the Western Federation of Miners at the time of the Steunenberg assassination, was the most cautious and moderate of the three inner circle members facing murder charges. While Haywood and Pettibone were associated with the most radical ("the revolutionists") wing of the WFM, Moyer generally aligned himself with "the reformists." Moyer's advocacy of negotiations and arbitration with mine owners brought him into frequent conflict with Haywood, and their bad feelings only seemed to worsen during their common incarceration. By December, 1906, Moyer and Haywood were no longer on speaking terms. Detective McParland saw Moyer as the weak link among the three defendants, and had agents discuss with him the possibility of turning state's witness.  Moyer strongly considered the suggestion, but ultimately took the stand for the defense, answering questions in a self-possessed manner and denying ever having discussed Steunenberg's murder with Harry Orchard. (Orchard testified that Moyer said the murder would have "a good effect," and would "scare" other politicians opposed to WFM goals.)

Moyer grew up near Ames, Iowa. His mother died when he was one. He had only four years of formal education.  At age 16, Moyer headed west, landing a job for a year as a cowboy in Wyoming. In 1885, after driving a herd of cattle to Chicago, he decided to settle there. After serving a year in the Illinois State Penitentiary for robbery, Moyer went west again, this time finding a job as a miner in South Dakota's Black Hills and joining the WFM. In 1902, Moyer was elected President of the Federation. Two years later, when martial law was declared in Colorado because of unrest in the mines, Moyer was charged with printing and distributing an illegal poster and held in a Telluride jail.

Moyer was arrested on charges of conspiring to murder Steunenberg after boarding "the Deadwood Sleeper" at the Denver depot. At the time of his arrest, Moyer possessed $521 in cash, a .44 revolver, and 100 rounds of ammunition. He apparantly was fleeing Colorado and his likely arrest, probably hoping to reach Canada.  Moyer took his arrest and trial the least well of the three inner circle members. He was often observed crying in his cell, walking with a gaze fixed "ever downward," and nervously fidgeting during trial testimony.

When both Haywood and Pettibone were acquitted by juries, the government dropped all charges against Moyer.