First and foremost - the shooting WAS justified. That makes the need to discover who fired the fatal shot moot. Therefore, the fact that they could not identify who fired the shot was not a factor in deciding whether murder charges were laid.
Anybody that thinks someone is justified in shooting at police officers who first knock, identify themselves, and then are forced to batter the door down to legally enter a house under a search warrant, are dreaming in technicolor.
Wildly shooting at police officers who identified themselves as police officers with your girlfriend standing beside you in a hallway is incredibly stupid and dangerous.
What did he think was going to happen? Did he think he was going to kill all the police officers before they returned fire?
He obviously was seriously deluded and/or hated police. He certainly did not care for the safety of his girlfriend.
The only person responsible for the death of Breana Taylor was her idiot police hating boyfriend.
Legally justified shooting. Period.