Most likely the first film to ever use follow-focus. D.W. Griffith convinced his most trusted cameraman, G.W. Bitzer, to fade out the background when the three gangsters walk towards the alley in the opening scene. During this era a cameraman was judged on how sharp and clear his picture was, so Griffith had to take him to an art museum and show him how the background was out of focus and the characters were in focus to convince him to do the effect on the shot. The focusing method is still used.
Widely considered the first modern American gangster film. Gang leader The Snapper Kid - performed by the tragically short-lived actor Elmer Booth - provided a cocky, enterprising prototype for later Hollywood actors (Cagney, Bogart, Robinson, Raft, etc.) who played hoodlums onscreen through the 1940s.
In a street sequence, a young girl can be seen staring at the camera. This was not a mistake; D.W. Griffith had noticed that, in documentary films, people tended to stare at the camera, and felt that having her do just that would make the scene feel more realistic.
At six minutes into the film there is a dance hall scene.On the right leaning up against the wall standing in profile is a tall man who looks like D W Griffith. Since he made appearances in other films, maybe it is him. It certainly looks like him.