The warrant was legal.
The boyfriend's response appears to have been justified, as well.
For him, it all comes down to did he know they were police, or should he have a reasonable belief they were police.
Home invaders yelling in the middle of the night and breaking down doors is pretty common.
Even home invades yelling "police" happens repeatedly.
He had no criminal record, and he dialed 911 immediately after the shooting.
It was recorded. The operator asks him who shot his girlfriend. He basically, sobs hysterically, I don't know, I don't know.
Considering the case and all the press, it will be hard to find a jury which would convict, imho.
You can’t shoot through the door when someone knocks on it and states they are the police.