I have been saying something along those lines since Wednsday. Looks like a couple here disagree but at this point it seems the most likely.
I think he thought of the victims as a sacrifice that needed to be made to make us all safer by showing how deadly guns are. I think he was triggered last year when Trump won the election. Would not suprise me if in the past he lost someone to "gun violence".
Seems like when it came to "gun violence" his family was on the safe side of the gun.