Substitute "killed without a court decree" then. One justification for use of deadly force is that your own life is at imminent risk (more technically, that there is reasonable fear of imminent serious injury or death).
The case that you cited was that deadly force can be used to prevent escape. My contention is that resort to arson was had, in order to kill Dorner. The police deny both. They deny an intention to set fire to the structure, and they deny an intention to kill Dorner. Neither of those denials is credible. However, you are arguing that both of those action are legal and justified. IOW, there is more than one argument going on here. Not even the police are adopting your point of view.
I think the cops are not owning up to deliberately burning the building to avoid PR problems, not legal ones.
One deputy had already been killed. So the perp was already a known killer.
He refused to surrender. He could have picked off another officer in the siege.
Best to end it, since he had said in his manifesto that he would not be taken alive anyway. No point in giving him the chance to take another cop with him.