I call bullshit on this story. Video of the incident or it didn't happen. Pictures of the aftermath aren't good enough. All Fed govt bldg have cameras facing in every direction and on every corner. Also, every Fed bldg has direct line comms/panic alarms hardwired into the local LEOs and nearest FBI offices, so the chances of something like this happening are slim to none.

Unless you're a highly trained individual who also has a fair bit of money, firing 500 rounds before being confronted or taken out by LEOs is impossible. And by highly trained, I can only think of a handful of people with the necessary shooting skills capable of something like this, and absolutely NONE of them are unstable enough to even attempt this.