THIS IS NOT CONFIRMED INFO: I may be getting this totally wrong, and I have no links...BUT I heard various discussions on the local news here (Seattle) which made me think that Josh had been having the supervised visits at his pastor's house (after complaining that prior visits, held somewhere where other families were as well, were not private enough). And that the fatal visit was somehow finagled so it could be at the rental house - like, the pastor thought that had been approved but it wasn't? Or something like that. In any case, I was left with the impression that the visits had not been occurring at the rental home. AGAIN, this may be my faulty understanding or a misconception. There was so much coverage here and, like everyone, I was in shock so maybe I got it wrong. But if it's correct, that would explain why CPS never had a chance to see that the house was staged. (I'm left wondering why he would bother to stage it if he had his horrible plans in place...but maybe he didn't plan too far in advance....shudder. Who can understand this??)
Also, if Alina did help him stage it, I would think that means only that she was doing usual Powell stuff: putting one over on The Man. I'm sure it never would have occurred to her that anything horrible was going to happen to the boys. But the Powells clearly don't like following rules or being told what to do. IMO!