Don't blame they one bit.
The guy had just murdered several of their colleagues and had made it pretty clear he was going to murder more, if given the opportunity. They got him the only way they could. Leave the uniforms and affiliations out of it for a moment. He'd just murdered their friends. As human beings, what do you expect them to do?
Then. I think it seems pretty obvious this was a form of "suicide by cop", going out in a blaze of glory - he wasn't going to come quietly. Any attempt to approach him to carry out an arrest would have led to even more deaths, any attempt to seal the area would have given him the opportunity to turn it into a shoot out, either when he shot at people attempting to seal it, or when he attempted to leave.
I'd have done exactly the same.