The gun was drawn before the victim hit the spray. Doesn't look justifiable to me.
Some blogger broke down what happened (based upon several videos).
There was a BLM guy apparently trying to pick a fight with several counterprotestors.
BLM guy baited the victim, who didn't bite.
The shooter approached the group, the victim peeled off to confront him.
The shooter tried to grab for the victim's mace can, the victim slapped him, and began to back away.
The shooter pulled out his gun, the victim brought up his mace can and both went off simultaneously.
Needless to say the gun was more effective. Second degree murder, open and shut.