The North Hollywood robbers had illegally modified their weapons to enable full-auto fire. Since well before 1997, modifying guns like this has been a federal felony that gets you a ten-year prison sentence. That's a prohibition that predates the Assault Weapon Ban, which had nothing to do with full-auto weapons.
The AWB has since expired, and doing your own full-auto conversion will still get you ten years in the slammer. You can buy a full-auto weapon, but only after an extensive background check and approval of your local sheriff, if your state allows it, and only if the weapon was manufactured before 1986.
The movie Heat, of course, also had its robbers using full-auto. Incidentally, the movie came out before the North Hollywood robbery; many people have actually blamed the movie for inspiring the real robbers, one of whom owned a copy of the movie!
https://en.wikipedia.org/wiki/North_Hollywood_shootout
