It may be true that the homeowners were involved in some illegal activity, that is, selling Marijuana, but the kid engaged in some armed robbery and paid the price. Plastic gun or real gun, no matter, armed robbery is what it is.
The comments on the article are saying this kid was more of a victim than those he was attempting to rob, so how's that? He was on the beginning of the path to destruction, and it came a bit early. Sad to say but it might be good that his criminal career was cut short.
The kid should not have been involved in stuff like that, he made some choices that ended up with deadly consequences.