What do you think it would take for someone to lose their temper so badly that they picked up an object and bludgeoned someone they knew well, possibly even loved, and killed them?
What makes people fly into such a rage that they would resort to murder?
From the male perspective.... rejection. I remember when I was a kid, and me and my cousin were trying to meet these two young ladies that lived near my cousin. When we finally approached them, they were not interested in us. I remembering wanting to punch a car window, and thought if I did, I could break it. Attractive women bring out an incredible passion in young men, and rejection intensifies that passion.
We know that there was a fight, and Allison fought back well, so it seems likely a man would have to escalate the fight to a higher level, growing in rage as she scratched him, and fought back well. It might have just been a momentary temper tantrum, which unleashed the demons in this person. Maybe they were abused in their youth, and the fight brought back their lack of impulse control, which they had hidden for years. I hear it is common amongst people in prison, a complete lack of impulse control, as if they were standing by and watching themselves go into fight mode.
Possibly the person was extremely remorseful after the fight occurred. So often in murder cases (I watch about on TV), it seems like the death was an accident, or not intentional, yet people are always looking for the villain, the shadowy figure with evil intent. Sometimes when the case is hard to solve or perplexing, it is because there was initially no bad intent, but just snowballed into a crime of passion, or even an accident.