I don't think it was made public if JP did undergo a psych evaluation previously, (HIPPA laws?) but I would certainly hope he did at some point...surely.? Let's be honest...after the beanie cap interview, we all were concerned about all the red flags .. questioned his mental health status. Then after his move to WA and no apparent negative reports (other than him keeping the children from the Coxes) the discussion subsided...until his father's arrest.
Somehow, all this relates and goes back to his relationship with his father.., his manipulation and puppeteering of JP all his life (JP was the oldest of the boys); his father's strange view on sexuality, women and lack of proper boundaries. And for those who have experienced the Chantrey site, his father's own chaotic family's dysfunction.
I agree, this would have happened....eventually..no doubt, imo. Even if the Coxes were awarded full custody, with or without JP having visitation, imo, JP would have taken them...and maybe the Coxes or whoever was with the children at the time he would have decided to put into his plan.
IMO, there isn't one thing that caused this actually, but a string of unfortunate events over the years, involving many people, mis opportunites to get help, etc. Do I blame JP, ultimately, yes; but I don't think JP had the know how to even help himself and hid his deficiencies very well....and/or was so blind sighted by his father's delusional parenting, that any help that would have been offered or was....would was negated and ignored. Even if he wasn't the one to actually "disappear" Susan, but knew his father was involved, he wouldn't betray his puppet master or all the dark secrets he harbored about all his family. JP couldn't recognize true love...control to him equalled love. "If you love something, set it free." He had no concept of it. He was one, very, very sick puppy.. and unraveled. It was just inevitable,, unless he was locked away; with evidence of Susan's harm or his mental instability. JMO, IMO, etc.