He thought it was the real thing. Seems to justify this as nothing more than a fatal mistake.
The cop did overall the right thing. Imagine if it was a real hand-gun, opening fire on both the cop and students. He would of been absolutely smashed if he hadn't of done what he did. Not to mention all of the deaths that may of occurred. And may I say to the people slamming him for not realizing it was a pellet gun... In that situation, you don't stop and analyze what make of gun it is... You need to fucking act, fast. It could be over in under a second. The cop needed to make a split-second decision, and given the rough area, the gun LOOKING real, and the fact that the gun is even in the school, anybody would of instantly thought 'hostile.'
And to put the icing on the cake, he didn't whack out his desert eagle to blow the kids head off, he smartly taze'd him. It's not SUPPOSED to be fatal, it's just purely bad luck that it was. I'm trying to paint a picture of the situation, did the kid seriously expect anything different? I assume he was waving the gun around with the cop in the same hallway, and I did a little digging on the school, apparently it's a tad on the rough side. Go figure.
Cut some slack to the police officer, anybody would of done what he did in his situation, maybe even worse than he did. He followed all the right paths, and took all the right measures, it's just a shame things ended up the way they did.