In late 1921, along with former Auburn inmate Charles Loeber, Chapman and Anderson began committing armed robberies. On October 24, the three men forced a U.S. Mail truck to stop at gunpoint on Leonard Street, successfully taking $2.4 million in cash, bonds and jewelry. Their identities were unknown to the police for months, and Chapman lived the life of an aristocrat, residing with his mistress in New York's fashionable Gramercy Park neighborhood. The three men were eventually arrested by United States Postal Inspectors William Doran, Jim Doyle and William Cochraine on July 3, 1922, after Chapman attempted to sell Argentine gold notes (stolen during the Leonard Street mail robbery) to an undercover postal inspector posing as a stock broker. Chapman made headlines when he briefly got away from his interrogators at police headquarters, but he was caught before he could leave the building.