M-16s in the MLB

I was meeting with a professor in the MLB today to discuss a research paper that I am currently writing. As we are sitting there with the door open to his office (school rules), 4 huge police officers go running by with bullet-proof vests on wielding M-16s. The last cop pokes his head into the office:

Cop: "Have you seen anyone with a gun?"
Prof: "Not today."
Cop: "Close the door and lock it." The cop runs after his buddies.

We sit there baffled for a minute, having just had an M-16 pointed in our faces in the middle of a friday afternoon in a school building and we continue to talk about the paper for about 10-15 minutes. The cop then returns, lightly tapping on the door, giving us the all clear. He then proceeds to explain that it was a false alarm -- a boy was dressed in a spiderman costume and ski mask for a presentation and someone called the cops. It's still unclear as to whether this "bandit" had a fake weapon or not...