From Wikipedia, the free encyclopedia Horace McMahon (May 17, 1906 – August 17, 1971) was an American actor. McMahon was born in South Norwalk, Connecticut. He became interested in acting when he was a student at Fordham University School of Law. In his early career he mostly played thugs or jailbirds, but in 1949 he starred in his most acclaimed role, as Lieutenant Monaghan in the drama play Detective Story and in 1951 he reprised his character in Paramount Pictures' film version Detective S...