Probably got tired of her nagging him.
You'd be surprised at what some sons have done to their overbearing mothers.
I once saw the crime scene photos of an instance where a man in his 40's killed his mother. He stabbed her 20+times, hacked at her head with a machete (sp?), and finally decapitated her with a chainsaw, because he couldn't get her hear off with the machete. Turns out the man met a woman, and wanted to move out of his mother's house, and move in with his new flame (possibly his first EVER). The mother would hear nothing of it, and homeboy SNAPPED.
When you see something like this, usually the murderer has a HUGE amount of animosity built up.
"Naggy" mothers get it BAD..............
As do beaten ex-wives of former NFL superstars.