The teenagers were acting in a criminal manner. As a result, it's difficult to defend them, and a bit less difficult to feel sorry for them.
However, the homeowner/shooter sounds psychopathic, based on what I've read in the article. And, by psychopathic, I mean psychopathic in the proper usage of the term: callous, unempathic, calculating, and sadistic.
Did the teenagers deserve to be shot? I don't know, but I know it's difficult to argue against them crying foul if they were.
Did the homeowner act criminally? Again, I don't know - I'm not a cop, a lawyer, a judge, or a jury - but it sure seems like he acted immorally. From his description, he seemed to relish in executing two trespassers - which goes way beyond what I think is the spirit of the law, which is that you are allowed to defend your home/your life.