When Warner Brothers re-released this movie to theaters in 1948, a new opening scene was added to explain that the 1935 movie did not reflect the FBI of the late 1940s. David Brian plays an FBI official addressing a group of new agent-recruits (among them Douglas Kennedy), for whom the old movie will be a history lesson.
In this film, which was made after one of the many "censorship" reforms, the gangsters are never seen using one of the more common gangster weapon: the Thompson Sub-Machine Gun. In an effort to curb the violence in movies, the new "production codes" forbade the use of the weapon by gangsters on camera for fear that it would corrupt the youth of America (a fact explained in the Les anges aux figures sales (1938) DVD documentary). This is especially evident during the lodge shootout. All of the cops and FBI agents have Tommy guns, 12-gauge pump shotguns, and automatic pistols, while the gangsters have only revolvers and lever-action rifles.
Two of the prominent action scenes in the film are based on real events. The rail station shootout in which gangsters free Danny Leggett, is based on the famous "Kansas City Massacre" in which gunmen attacked FBI agents and local police as they were transporting federal prisoner Frank "Jelly" Nash on June 17th, 1933. In that incident one FBI agent (who was unarmed, as were all agents at that time), three policemen, and Nash himself were killed. As shown, this was the incident that increased the power of the FBI and turned into the agency it is currently. The shootout at the lodge was based on a battle between FBI agents and a gang that included John Dillinger and Baby Face Nelson on April 22, 1934.
Initially, FBI Director J. Edgar Hoover and U.S. Attorney General Homer S. Cummings disapproved of the film. Their primary reason was that it portrayed an FBI agent as insubordinate (i.e., McCord having to deal with a recalcitrant Davis) and acting on his own (Davis leaving the hospital to find Collins). However, when the movie became a success, Hoover and Cummings realized that the film could be used to promote the image of the FBI, and they changed their minds and began openly endorsing it.
J. Edgar Hoover, Director of the FBI, personally approved the script for this movie. He even assigned FBI agents to monitor its production and ensure that it was accurate in every detail. When it grossed over $1,000,000 (an astronomical sum for a film in 1935), he was extremely pleased. There were two famous federal law enforcement agencies in the early part of the 20th century: the "G-Men" of the FBI, who worked for the Justice Department, and the "T-Men", who worked for the Treasury Department and who were responsible for bringing down Al Capone. Hoover was intensely interested in his "G-Men" winning the publicity and popularity rivalry. This movie certainly helped.