Something that I strongly suspect but can find no documentation to back up is that the sexual pursuit of pre adolescent children is virtually always a Solitary Activity.
I can not think of one case where anyone involved in such activity work in a team (can anyone provide an example). Sex crimes in general are usually committed alone an it is rare for someone to caught because someone who was aware of their activities "ratted them out". There are are some exceptions for rapist and I am aware of one serial killer in LA who worked with accomplishes to target teenage boys, but never younger children.
It think the stigma might be so great and the consequences so severe if caught that perpetrators of this crime operate completely alone. Therefore I believe that none of the scenarios involving anyone else will apply and nobody is likely to come forward with the critical evidence that will put Heinrich away. That does not mean, however, that people who knew him and were aware of his day to day activities in 1989-90 might still be able to provide important information.
I do not think there was more than one re Jacob, but the Hillside stranglers were cousins and worked together. Their victims got younger from the adult women.
There are more but cannot remember.