Gerard Butler gained twenty-five pounds for his role, as recommended by director Christian Gudegast.
Christian Gudegast's original cut of the film was closer to 160 minutes and featured a different ending.
The film was in development for roughly fourteen years, where director Christian Gudegast and a writing partner had a blind deal with New Line Cinema in 2003. The project was also later supposed to be distributed by the now-defunct Relativity Media at one point as well.
Amongst the cast, there are four UFC fighters: John Lewis, Max Holloway, Oleg Taktarov and Michael Bisping.
In the closing credits the $100 bill has the serial number DOT00002018, for Den of Thieves 2018 the release year.
Prior to filming, two separate boot camps were run in order to get the cops and the robbers in shape for their respective roles with both groups training separately to enforce a rival atmosphere. Interestingly, each group was trained differently by military consultant Paul Maurice.
Gerard Butler and his crew are loosely based on former ATF agent, Jay Dobyns, who consulted on the film. Dobyns is best known for his undercover work and his willingness to infiltrate crime organizations, much like Gerard Butler's character. Dobyns makes a cameo in the film at the bar Donnie works at in LA, closing his tab at the bar.
Eric Braeden (Ziggy Zerhusen) is the father of the writer and director Christian Gudegast.
After the initial robbery Ray Merrimen (Pablo Shreiber) tells Bosco (Evan Jones) "Be careful with those guns, I don't want any accidental discharges). In 8 Mile Evan Jones plays Cheddar Bob, B Rabbits childhood friend who shoots himself with his own gun.
Although set in Los Angeles, a vast majority of filming took place in Atlanta, to take advantage of the state's tax breaks.
This was the second time Pablo Schreiber played a thief masquerading as an armored security guard. The first time was Person of Interest: Matsya Nyaya (2012).