Smith had been visiting neighbors when he saw Kifer, whom he suspected was responsible for the burglaries, driving past his home. He commented that he needed to get ready for her and went back to his home. Upon entering his home, Smith turned on a recording device he owned. He removed the light bulbs from the ceiling lights and positioned himself in a chair that was obscured from view. He heard the window upstairs break and Brady climb in (captured on audio).

There may have been a window from the garage to the house or something, but it clearly says they broke a window, entered his home, and proceeded to the basement where they were shot. He had previously been burgled in the garage too, which Wikipedia says he was unaware about until police found evidence of a prior burglary. The house had been burgled previously as well, which is why he was looking out for people casing his house.

I hope none of this comes off as a defense of that asshole, but facts matter, and those teens did commit a crime. I don’t think they deserved to be executed for it, but he was within his rights to defend himself when they broke in to his home. He was not within his rights to execute them after the threat was over.