Very similar thing happened here in Tyler, TX a few years back on the Court house lawn. The guy had full body armor, armed to the teeth.
Bullets were raining in the court house and out. The Sheriff's deputies were helpless.
A freind of mine, Mark who ran the indoor range here was a superb shot with his Officers model. He tried to stop the guy from cover, a vehicle. He shot 2-3 times I believe, but no effect. Mark did not realize the guy had Body Armor. After the guy got hit, he walked over to mark and blasted him with his assault rifle and while he was down gave a coup 'de grace for good measure.
The whole incident really rattled the Judges and proscecutors pretty bad as you would expect, feeling helpless and all.
Now there are AR-15's on every floor in the court house available not only for the Sheriff's office, but for Court Officials as well.