How would the killer know his initial plan to first do one "head trauma knockout" as his google search showed, followed by strangulation to do the killing wouldn't work and he would then have to resort to beating MY's head and face over 30 times? Think he knew while creeping up those stairs that's what was going to happen?
CY was likely asleep in her bed. Had his strangulation plan worked his daughter probably would not have woken up. But 30+ blows makes noise.
You bring up an excellent point.
The initial killing was supposed to be strangulation, when that failed, she was beaten.
Why in the world does someone have to look up trauma to the head, when anyone knows if you hit someone hard enough or long enough, that they will die?