TS, you are right on the money. Lets play the scenario. You hear glass break, calling 911 would be the first option. If not already armed, you would do so. How about verbally challenging the intruder? Something simple like " Who's there?" or the ol' " Get the f--- out of my house!". Most burglars are property thieves. A home invasion is another animal all together. Ok so this individual/psycho lies in wait for an intruder, then ambushes one, and despite gun shots, and the sounds of a mortally wounded person we are expected to believe the second intruder just waltzes right into his sights. Sounds like he had a plan and followed it to the end without regard to the actual circumstances.
"Serial killers differ in many ways, including their motivations for killing and their behavior at the crime scene. However, attendees did identify certain traits common to some serial murderers, including sensation seeking, a lack of remorse or guilt, impulsivity, the need for control, and predatory behavior."
http://www.fbi.gov/stats-services/pu.../serial-murder
The method of his description of what happened added to the manner of his actions appear to fit the above traits.
Hope he burns, slowly.