The holder of a Columbia law degree, he began writing plays in the late 1920s and later wrote radio scripts, including the famous Orson Welles broadcast of H.G. Wells's War of the Worlds. In Hollywood from 1940, he contributed many literate screenplays to films, mostly alone, some in collaboration. In 1951 he was blacklisted by the industry under pressure from the House Un-American Activities Committee. He used the pseudonym Peter Howard for screen credit on Joseph Losey's (under the pseydonym Joseph Walton) British-made THE INTIMATE STRANGER / FINGER OF GUILT (1956), but didn't resume screenwrting under his own name until the early 1960s. Occasionally a playwright, Koch wrote the books The Panic Broadcast and As Time Goes By: Memoirs of a Writer in Hollywood, New York and Europe.  Nominated for Writing (Original Screenplay) 1941: SERGEANT YORK (w. Harry Chandlee, Abem Finkel & John Huston)  Writing (Screenplay) 1943: CASABLANCA (w. Julius J. Epstein & Philip G. Epstein) 2 nominations, 1 Award