Cherry-picking single, isolated incident does not change mountains upon mountains and decades, upon decades of statistical data that proves you wrong. This one man may have been capable of killing a person with his bare hands, but that doesn’t change the fact that literally anyone is capable of killing another person (and themselves) instantly with a gun. 
I always find it, particularly strange when someone claims to know the mind of someone who has “snapped to this extent“both claiming to know what they think, while simultaneously, claiming that you can’t know what they might do. 
The fact is, you can’t claim to know what another person thinks. But the statistical data shows that when taking a gun out of the situation, it’s far far far less likely that the murderous act would be carried through simply because it’s no longer as easy.