I believe he planned, monitored the victims and carried out a blitz attack. If all three victims were sleeping, it could be carried out quickly, without screaming and more importantly - the chance of anything going wrong. One blow is all it takes to subdue a victim and if they're sleeping... It's quick, violent and effective.
I have always contended that this horrific crime was simple in its motive, planning and execution. If it was more complex, LE would have released more information and taken longer for an arrest.