When Christopher Walken works with guns in film, he checks them himself before each scene for safety reasons and his own personal ease. During the scene when Sean Penn sticks a gun in Walken's face, Walken checked the gun before the scene started. Before the director had the chance to say "Action", Penn ran off camera and shouted, "Give me the other gun!" He immediately returned to Walken and started the scene. This is the cut that made it into the movie, and Walken was really terrified.
Actress Eileen Ryan, who plays grandma, is actually the real life mother of the Penn brothers Sean Penn (Brad Whitewood, Jr.) and Chris Penn (Tommy Whitewood), but plays not their mother but their grandmother.
Based on the actual crimes of Bruce Johnston, Sr., in Chester County, Pennsylvania.
The role of Brad Whitewood, Sr. was originally offered to Robert De Niro, who turned it down because he felt the character was too dark.