Marc Porel was originally offered the role of Giulio Sacchi. Director Umberto Lenzi had a meeting with him and found him to be "unreliable from both a human and professional point of view." Lenzi told the producer "It's him or me." The producer asked Lenzi if Tomas Milian was OK. Milian's conditions were reasonable so he got the part.
Director Umberto Lenzi stated in an interview that his first meeting with Tomas Milian for this film was really difficult because Lenzi felt Milian didn't trust him. Milian had heard rumors that Lenzi was an impulsive, hotheaded director but in the end Lenzi felt that Milian got that he was the right director for the job. This started what Lenzi called a "love-hate" relationship between the two that would continue for a total of 7 films with the actor.
American actor Richard Conte was originally cast in the part of Commissario Walter Grandi. Conte however died shortly before filming began and production could not be halted. The first available actor for the part was Henry Silva. Silva at the time was mostly known for playing villains and killers so director Umberto Lenzi had to work hard to try to make him fit the character of a cop.