I've got a propane-powered "AirSoft" ("PropaneSoft?") Colt MKIV clone that looks and hefts so realistically that I'm damned glad it does have a non-removable plastic red tip on it.
Just from currently-available information, I don't know if this incident is justifiable legally, but putting myself in the Officers' places on the overall fact pattern, and with all that's been going on with these school attacks, I can sure see it justifiable emotionally. Kid with what looks like a rifle (or, for that matter, even an adult) waves it around without muzzle training, and I can understand the "condition red" muscle reaction to it.
On the other hand, just from assorted videos I've seen, mind you, I can understand the confusion of the "suspect" under the conflicting commands hollered by the police.
"Drop the gun," "Hands in the air," "Get down on the ground," etc. all coming at once from different Officers, can result in an unthinking "Huh?" and turning-around response which would lead to those muscle-reactions. I don't know if it's procedurally possible in a tense active situation, but maybe there ought to be only one designated officer who shouts commands in situations like these.
Yeah, I know, an extra layer of complexity added on to a "situation," but it might be worth thinking about.
Terry, 230RN