After leaving the Army, Roberts returned to his criminal activities, and in partnership with Jack Witney carried out "dozens" of armed robberies, targeting bookmakers, post offices and banks. He said, "The most I earned was £1,000 from a single job. Witney was the eldest, the boss: he knew the best places to rob. Duddy joined us later." In 1959 Roberts and an accomplice posed as tax inspectors to gain entry into the home of an elderly man. The man was bound, robbed, and beaten about the head with a glass decanter. Roberts was arrested, and at his trial the judge, Mr Justice Maude, said, "You are a brutal thug. You came very near the rope this time. It is to be hoped you do not appear before us again." Roberts received a sentence of seven years.