Of course the castle doctrine is relevant, but I don't think this shooting is justified under the castle doctrine. The castle doctrine states that you have no duty to retreat within your own home, and that you may use deadly force when you reasonably fear imminent death or serious bodily harm. Mere perception of a threat is not enough - it must be reasonable, and it is going to be very difficult to convince a judge or jury that you reasonably feared imminent death or serious bodily harm with a locked door between you and the source of the perceived threat.
Curiously, do you believe George Zimmerman was guilty?
Absolutely not. That was a clear-cut case of self-defense, and I believe that Angela Corey committed prosecutorial misconduct by bringing charges against Mr. Zimmerman.
Thanks for being calm and reasonable.