I don't feel bad for the officer killed at all. If you do something stupid to get yourself killed then I am not about to shed a tear for you. Kicking someones door in, in the middle of the night with a no-knock warrant is that something stupid.
Just because someone is sworn in and wears a shinny piece of metal, does not mean said person is above the law. It is very clear what happened here. You have two overzealous detectives, moving on the word of an informant, waking a Judge up to get a warrant signed, without investigating their informants claim properly.
They moved on their warrant, alone, in the middle of the night, on a fella who is already on edge since is place was burglarized a few days earlier. Rather than making a knock warrant with some uniforms as back up, they decided to make a no-knock warrant alone. A stupid thing to do, valid warrant or not.
The end result is what you have happening here. It is the same thing that happened in Atlanta with that old lady. Except in that case an innocent civilian ended up dead for simply defending their self and their property from who they saw as intruders in the night.
While I won't go as far as to say, "good job Joe citizen" in this case, I also wont feel bad the officer was killed. The way I see it, him and his partner made a chain of poor choices that night. The end result ended up in someone being killed and another persons life now in jeopardy. Now the surviving officer needs to cowboy up and do the right thing here. So that another life is not taken, because of a stupid choice made by him and his partner.