Most of the bloody gunshot wounds were done with squibs, with a handful of CGI one also added. In the commentary, Wayne Kramer mentions that Bruce Altman was terrified of the squibs because he's never been strapped to them before.
Paul Walker's brother also appears in the film. In an early scene the path of a bullet is re-traced going from one house to another - the Paul Walker character appears in each house. The Paul Walker character sitting at the dinner table in one house is actually Paul Walker's brother.
When Oleg says he listens to "Kvasha", this is a direct reference to not only the music type, but also Oleg Kvasha who first played for the NHL team Florida Panthers back in 1996. The first name "Oleg" also happens to be Cameron Bright's character's first-name: Oleg Yugorsky.
One of the main characters' name (Joey Gazelle) played by actor Paul Walker could be derived from a character in the graphic novel 'Stray Bullets' where Joey (Gazelle) is a little kid in a criminal domestic environment.
The character of Detective Rydell (played by Chazz Palminteri) is an inside joke by writer/director Wayne Kramer as a tip of the hat to the film THE COWBOYS. The character of Anzor in the film is obsessed with the John Wayne film THE COWBOYS, specifically the part where John Wayne is shot in the back by Bruce Dern, which later becomes Anzor's own fate. The director of THE COWBOYS was Mark Rydell - therefore, Detective RYDELL.
This is the second film starring Cameron Bright to feature a clip of John Wayne getting shot. In Running Scared, the clip is from The Cowboys (1972). In Thank You For Smoking (2005), the clip is from Sands of Iwo Jima (1949).