I've only just started thoroughly digging, but where I'm at at the moment, I do think JDI and PR eventually helped stage.
I think PR grieved heavily. JR is a narcissist through and though. Upon meeting Patsy his own reflection was he didn't find her attractive but admired her wit and humour. He tends to base his assessment of quite a few women on their attractiveness. If he initially didn't think PR attractive, why would her find her so after her body has been through hell and back, she's lost her hair and by the sounds likely has considerable scarring to her torso area from the operations she underwent as a result of her cancer.
She cared about appearances. I know the inner turmoil I went through with severe stretchmarks after pregnancy, never mind being opened up, taken apart and put back together again, I doubt she opened herself up physically to JR for more criticism. She seemed like she had some histrionic traits, which includes passive aggression. Can we assume that JR the narc had PR not only doing what she could to please him, but also went out and spent willy nilly as her own form of passive punishment towards him?
I think JR assaulted sexually abused JBR, initially maybe in the kitchen after giving her some pineapple. She tries to escape, he grabs her and she hits her head hard, or he hits her, maybe he throws the torch to stop her but throws it too hard, knocking her unconscious. JR panics, tries to wake her unsuccessfully. He's frantic, thinking what have I done, I have killed herHe wipes down the bowl and puts it back in the fridge, he takes her down to the basement and places her on the ground out the front of the WC. He's tries again to see if she responds to pain, he pokes her, nothing, he burns her face with a cigar, nothing. He's carefully going through his options, what injuries does she have, his marks are all over her, she has been molested, this cannot come back on him in under any circumstances, how can he remove himself from the equation? PR notices JR has left the bed, BR is disturbed by PR looking in to see if JR is with him. She sets BR up with some tea and the remaining pineapple telling him to stay put, she wanders around the house, she can't find JR or JBR, so heads down to the basement after seeing the lights on. She makes her way down the stairs, and screams. She throws herself on JBR, JR instructs her to go get JBR new clothes whilst he cleans her down. She bends to the will of this man. She brings the clothes and hands them over as he fixes the ligatures. She's out of her mind, probably running her hands up and down her arms trying to comfort herself. JR needs to keep her busy and her mind on the task, he gives her a brief rundown of what's going to happen and what to say in the RN. PR goes upstairs, sends BR to look for JBR's babrbie nightgown, she's wet herself again she tells him, then puts him back to bed then goes to find the materials, JR strangles JBR. PR wants to make sure she's cared for, wraps her in the blanket before they close the door but they don't have time to change her clothes again. Both need to take some time out before they call 911, JR isn't happy with the first RN and makes PR write a second, coaching her. They try to pull themselves together, JR tells PR to make the 911 call. BR still not asleep, hears the panic and makes his way down.
At this time, that's my scenario. Not very well thought out and lacking detail, my theory is sure to change some the more materials I look at but I still think he did it.