I guess I'm not OAF because I certainly would have perceived him as a potential threat - at the very least I'd have kept a close eye on him. As far as his toy being 1/3 the size of a real gun - what about these new 5.56 "pistols" which are much smaller than even M4s? Are you REALLY sure that it's 1/3 the size? Cops get crucified because in the few brief seconds they have to shoot/no shoot they can't tell a real gun from a fake gun. And that's NOT a criticism of cops; if somebody would point something that looked like a gun at me guess what? Game's on.
What better time to strike than at Halloween when so many people are in costume? Had action initiated, amidst all the ensuing confusion, which costume was the threat?