Very Sad !!! After reading further, and some of the comments, the kid was adopted by the father, I feel alot better. Not good, but it's not like he killed his own flesh and blood. I"m saying it's OK. I'm saying as infidel says above, there was not that Father/Son connection there. I'd like to think I'm connected well enough with my 16yo son, even dressed in dark clothes and a mask coming at me, I'd recognize his body structure, his movements, and his actions. I just think I'd know this was my son and not shoot him. And if it were a prank, he'd be getting a beat down anyway because he was raised, shit like this isn't funny and you don't do these things for this exact reason. He's been taught, don't be sneaking in and out of windows of the house, or sneaking in back doors, or coming in at wee hours of the night without calling and notifying me that it's a great way to get shot.
And if he was seriously coming at me with a knife, I'd have it away from him and he'd been beat senseless and in the hospital, but not dead.
Chances are this kid had a bad life in his past before being adopted, and actually probably was up to no good but still didn't deserve to die unless he really had intent of harming his adopted dad. That's the sad part.