In 1953, he and Ryan encountered Benny Russell outside the offices of Incredible Tales of Scientific Wonder. Mulkahey gave Russell a hard time about his nice suit and his drawing of Deep Space 9 before letting him go. Ryan wanted to arrest Russell, but Mulkahey was not as interested.
Mulkahey and Ryan were later responsible for the death of Jimmy, a young criminal and acquaintance of Benny. At the time of Jimmy's shooting, Russell tried to help him but was forcibly restrained by Ryan and Mulkahey, receiving a severe beating in the process. (DS9 episode: "Far Beyond the Stars")
In December of that year, James Wykoff requested Russell's police record from the New York Police Department. The report stated that Russell had attacked the police officers and brandished an offensive weapon. (DS9 - Strange New Worlds IV short story: "Isolation Ward 4")