Abel Fernandez's character was based on William Jennings Gardner, a real-life Native American member of Elliot Ness' "Untouchables."
Before performing the Kiss Of Death scene between Bruce Gordon and Frank De Kovo, some crew members, including director Phil Karlson, decided to make a joke to them. They told both Gordon and De Kovo separately that the other was gay. To put some "spice" and realism to the scene. After the take, everyone on the set laughed loudly and explained to Gordon and De Kovo.