I agree, It is really sad for the family of this guy, and I feel bad for them.
That being said, I feel WORSE for the millions of families who have lost a family member due to this CEOs sociopathic decisions.
I think you put it really well with the criminal comparison. This CEO was a criminal, just one that was above the law of the US, who was never going to be brought to justice for his crimes in any other way.
To add on to what you said, only the lower recievers for most guns have to be registered. Someone could hypothetically get every other upper part for a pistol or rifle delivered directly to their door or PO box with no questions asked, and then just hypothetically 3d print the lower reciever.