The movie was banned in Spain, which was still ruled by Generalisimo Francisco Franco, the fascist victor of the Spanish Civil War.
As they were not allowed by the Spanish government to film in Spain, Fred Zinnemann and Alexandre Trauner stayed for two days at the Frontón Hotel in Vitoria (now Vitoria-Gasteiz) and went around the city to get pictures and information about buildings and people trying to reach the "intimate heartbeat of the city" in order to later recreate them properly. No local newspaper took the news maybe due to censorship.
This went through several title changes. It was also known as " The 25th Hour ", " To Spring a Trap" and " Killing a Mouse on Sunday ".