If you look at what happened, it's clear that Kyle shot all three in order to defend himself. You would need to be deranged to think that he was some kind of active shooter that went out there to kill as many people as possible. The worry is that the jury will be bored by the defense, and that they'll be dumb enough to fall for the obvious bullshit the prosecution is saying. I think that if the prosecutor is able to get the jury to think just one of the shootings is unjustified, they'll decide Kyle is a murderer and assume he's guilty for killing both people and not justified for shooting the one-armed bandit.