Greenberg was Allen's assistant again on Bonnie and Clyde, which was directed by Arthur Penn. The editing of the ambush scene in this film in which Bonnie and Clyde are killed has been very influential, and Allen credited Greenberg with its actual "cutting". Greenberg was the associate editor for Alice's Restaurant, again directed by Penn and edited by Allen. By that time Greenberg's independent editing career had commenced with Bye Bye Braverman, which was directed by Sidney Lumet. Greenberg later co-edited Penn's The Missouri Breaks with Allen and Stephen A. Rotter.