It made me think of tire iron/baseball bat. If it was the flashlight (and it probably was), it would have had to be slammed with incredible rage and strength. Someone was probably in a fugue state when they did it.
The garotte (IMO) was added later to make it look like a sexual crime, but more importantly - to make it NOT look like an accident. Just a blow to the head would have immediately made LE look to one of the parents.
Another point that's always seemed obvious to me was Patsy's appearance that morning. Patsy wears "full" makeup, not just a little mascara and lipstick.
Now.....maybe there are high school-age girls who can do on that upon just waking up - but by the time you're in your late thirties - and having at most 6 hours sleep the night before after running around all day - it's highly unusual.
Most people need a shower or coffee or both before they can go through those machinations. Yet - she did hair, clothes and makeup before she even went downstairs. All this, when she was going to be travelling on a private plane and only her immediate family would be seeing her.
Now exactly incriminating - but added to all the other odd things - it adds up to her having been up all night.