While loosely--VERY loosely--based on the real "Machine Gun Kelly" (real name George Kelly), there are many incidents in this film that simply never happened. For one thing, the only time Kelly ever fired his machine gun was on on a firing range, and he certainly never killed or even shot at anyone, contrary to what is shown in this film. Also, the Kelly gang didn't kidnap a millionaire's little girl, as shown in this film; they kidnapped the millionaire himself, a wealthy brewer named Charles Urschel, and this is what eventually led to Kelly's capture and imprisonment. Also, he wasn't captured in a shootout with lawmen, as shown here; police and FBI agents in Memphis, TN, surprised him in the stairwell of a boarding house and he fell to his knees and screamed "Don't shoot, G-men!", thereby coining the name that FBI agents have been known by since then--an incident that is completely left out of this film.
At 3:00 Machine Gun Kelly and Howard enter the Lebanon Bank. As the door is closing you can clearly see a reflection of what appears to be Boom Mic on the glass door.