I do not agree with the castle doctrine. It’s too easily used to justify lethal force when retreat is an option, however self-defense is a valid justification and from the description given I think that’s completely plausible. An unknown person breaking the glass and potentially armed could be a threat. It sucks that a guy who possibly did nothing wrong has to defend himself in an investigation, but we should have a high bar on lethal actions for civilians and cops (the standard should be higher for cops).