The home invaders wore all black, masks, and one was armed with a knife while another had brass knuckles. "Exchanging words" is an interesting detail that lacks significant detail. That could mean just about anything from sitting down, having a chat over a hot cup of coffee or the exchange of threats and warnings within a small time frame before the shots were fired. I find the way you describe the shooting as if the home owner's son thought deeply before each kill to be a bit presumptuous and possibly disingenuous. That aside, I look at it like this. It doesn't take that much time to fire the weapon, one. Two, how is the son supposed to know what weapons the potential robbers have? These people could have possibly murdered or wounded him had he not fired. The repercussions of entering a home that is not yours should be steep, given that your entrance is unwarranted AND sinister. I see nothing excessive here except the tragedy of three boys led astray.