In MA, even if he is inside your home, you still can't shoot unless you are in immediate danger of death or grave bodily injury. There are a few states with so-called Make My Day laws that allow you to assume that anyone illegally in your home is a grave threat. But most states are like MA in that even inside your home you can only use deadly force if they are a deadly threat -- see my discussion of Ability, Opportunity, and Jeopardy above.
I'm not so sure about that. If they have a gun and are threatening to shoot you through the door, then you might be able to argue that you were, in fact, in immediate danger of death or grave bodily injury. If they just had a contact weapon (knife, club, etc.) then that would be a different story.
Imagine this scenario...
Drunk 15 year old breaks the glass and opens the door.
He is obviously drunk, slurring speech, stumbling, no weapons in his hands.
You have a drunk idiot in your house.
If that was the extent of the situation - would you feel that you are in imminent and unavoidable threat of grievous bodily injury or death?
In MA, even in that situation you must prove you were in Jeopardy.
Also consider escalation of force. Is it appropriate to shoot an unarmed intruder?
You yell at the guy and he still won't leave?
Is it really necessary to shoot at that point?
Even if "you get away with it" - is it really worth it?
Your name will be all over the internet and you and your family will go through hell even if you are not charged.
In college towns in MA, there have been about 3 police calls for drunks entering homes in the past 12 months.
None of those ended in death or injury.
If the drunk guy became violent and I was in fear for my life I would have to escalate my response.
It may take a while but this Chicopee guy will really feel sorry for killing this kid and it could take years off his life even if he is found not guilty.
I don't think he will be convicted of murder if he goes to trial.
He would more likely get convicted of manslaughter and get 10 years - out in 5.
He should plead this out and accept a 5 year prison sentence.