He went on to draw for Lev Gleason Publications' "Crime Does Not Pay" and "Black Diamond Western". As Rockwell told the story, samples of this work, which he supplied with his membership application to the National Cartoonists Society in 1952, caught the attention of Milt Caniff, the organization's president at the time. Soon afterward, Caniff hired Rockwell to assist on Caniff's classic syndicated newspaper strip "Steve Canyon", penciling and inking secondary characters and backgrounds; Caniff wrote, drew the main characters, and did finishing touches. He served as the uncredited art assistant on "Steve Canyon" for 35 years, continuing for a brief time after Caniff's death in 1988.