Extremely shallow, due to shock.
And in the state of mind they must have been in, they wouldn't know it if they knew it.
SuperDave, I respect your opinions very, very much--which is why I want to ask you the one question that still makes it very hard for me to accept the PDI-Toilet Rage theory.
According to this theory, PR suddenly and violently lashes out at JBR out of stress, irritation, annoyance or some similar emotion--and bashes her head with sufficient strength to dislodge a significant piece of her skull.
Panic stricken, she shakes and tugs at the unconscious child, causing bruising etc.
She screams for JR, who comes to her, assesses the situation, and the two of them decide that JBR is dead.
They further decide that they will have to cover up the crime, and start to do so.
Now--here's the hard part. Almost immediately, they decide to inflict a significant sexual wound on the--they think--dead body of their child!
Why almost immediately? The wound bled enough to leave a spot of blood in the second pair of underwear; further, forensic evidence suggests that blood was present on JBR's thighs and was cleaned up. There is no other wound on her legs, so the blood must have come from the vaginal wound. So the wound must have been inflicted before strangulation occurred, which according to something you wrote probably took place no later than one hour after the head blow.
But then, having done this horrific thing which could only be designed to make JBR's death look like a sex crime, the R's decide to make JBR's death look like a politically/personally motivated crime against JR, necessitating the writing of the ransom note.
Even if we say that they changed their minds again and decided to return to the 'sex crime' scenario, that doesn't explain two things: one, why they didn't change the RN, and two, why they didn't make at least some attempt to make the wine cellar crime scene look like a sex crime scene (e.g. removing the troublesome underwear entirely, staging the body to fit a pedophile scenario, etc.).
I honestly can't come up with any reason two shocked and panicked parents would very quickly decide that they had to inflict a sexual wound on their unconscious and apparently dead daughter. Can you help, SuperDave?