He hasn't been in the military for almost twenty years. He has spent most of two decades since in law enforcement. I think we can assume he has had masses of weapons training since and that he can understand the difference between self defence and intention to kill.
Interestingly, when you read that full research, which was produced for a law enforcement group, it was clear the people who organised it didn't like the outcome. So, they tried to trash the research. That is because it showed that even untrained civilians can assess the situation and manage to cease firing within the timescale that the agent had available.