Not surprising, considering how they've always played the PR game very well.
How many people know that when the G-men took out Dillinger, the case that made the FBI famous, said G-men shot a couple of innocent by-standers?
He kept his focus on the Italians and Sicilians in Chicago. In fact there are some very good analyses on the internet regarding the possibility that it was actually Dillinger who did the St. Valentine's Day deal, and quite possibly to help out his ol'buddy Elliot.
If Ness had been of a different ethnicity, e.g. English, Swedish, Finnish, Norwegian, German, Polish, Russian, etc., he might well have taken down Dillinger himself.