Personally I think the dad maybe did it, or I think whoever did it HAD to have connections with the family to know that they left. And for the serial killer that claimed he left those poor baby’s somewhere, did you check the place? You assumed he was lying but you could’ve still checked. I hope my words try to connect anything to find these baby’s.
I don’t think it was the Dad, because the dog was locked up. If it was the dad, then he wouldn’t have had to lock up the dog it had to of been a stranger. And I don’t think the guy who claimed he did it did it because if he was going to admit it he would have known where they were at.