Investigators say [the dead guy] was drinking and locked himself out of his apartment. He tried to crawl through a back window but it was the wrong apartment.The guy in the apartment he was breaking into thought - and reasonably so - that this was a home invasion. (Technically, it was.) He shot the guy in self-defense.
And yes, police are calling it self-defense. I mean, what would you do if someone was climbing through on of your windows shortly after midnight? I know what I would do.