Famed criminal profiler Dr. Forrest presents his learned opinion:

It may have been an intruder or the boy, but I've always had a sneaking suspicion that it was the mother: the "ransom note" was was probably written by her, with pen & paper from the house; the broken paintbrush used as the handle of the garrote was hers - therefore, like the writing materials, not brought in as part of a previously prepared rape/murder kit of the sort usually employed by calculating killers, etc. Additionally, I noted her distinct aloofness when speaking of the little girl, referring to her as "that child".

Patsy was clearly an anal retentive control freak, for whom even the tiniest detail had to be perfect: in one I think telling instant when she was emerging from an interrogation session, supposedly distraught and leaning on her mother's arm for support, she had the presence of mind to slyly clasp her mother's hand, thereby hiding a pack of cigarettes there.

Well, what the fuck could possibly be the significance of a trifle like that? I believe it - like many of her other uptight behaviors - showed her to be an extremely class conscious nouveau riche, painfully aware of her West Virginia origins: she no doubt understood that most of the rich folks she then socialized with and desperately wanted to be accepted by are far more health conscious and anti-smoking than those she grew up with, so she didn't them to see the cigs and think "hillbilly hicks".

And if the girl kept pissing the bed after repeated warnings, it would surely drive such a tightly-wound creature into a rage.

Then there's the way she tarted the little girl up for the beauty contests: adult makeup, very skimpy bathing suits. Perhaps she subconsciously hated her because she blamed her birth for triggering her ovarian cancer - or she may well have been molesting the kid herself because she was a deeply closeted lesbian: again, a religious fanatic like her would be boiling with shame & rage at such forbidden desires, and if she had a sick mind, she'd probably transfer those reactions to the victim. "You tempted me into this, you little slut...."