Before signing on to write radio shows for Orson Welles' Mercury Theatre, Koch had several plays produced under the auspices of the Federal Theatre Project. His best-known work for Welles was the notorious 1938 adaptation of "The War of the Worlds". With Warner Bros. from 1940, he wrote several outstanding films, notably "The Letter" (1940), "Sergeant York" (1941) and "Letter from an Unknown Woman" (1948), as well as collaborating with the Epstein brothers on the romantic classic "Casablanca" (1942) to which he reputedly brought a political edge by beefing up Rick's political past and romantic
