If someone breaks into your house and you feel like your life or someone else's life is in danger (which is probably almost always the case), I'm fine with shooting someone. If they die, then that's valid self-defense.
Once you have shot them and they lie bleeding on the ground, a "clean finishing shot" is not self-defense. It's murder.
Even in the Wild West of gun-loving Oklahoma, you can't shoot someone bleeding on the ground with a "finishing shot" and call it self-defense-
http://www.cbsnews.com/news/oklahoma-city-pharmacist-jerome-ersland-found-guilty-of-murder-in-killing-of-suspect/
Also, there are lots of other facts that make the guy sound like a loon: the fact that the guy parked his car 3 blocks away, had his house full of surveillance cameras and a cell phone jammer, was trying to hide the 1st body, and then waited until the next day to call the police. That's not the normal behavior of someone acting in self-defense.
It's kind of like when idiots run out into traffic. It's hard to be sympathetic to idiots when they get run over, but at the same time there's no open season for car drivers to run idiots over.