[@Redking0380], I believe I have an interesting connection suggestion for William with one of Cassidy's playbook histories:

"You used your powers on them one time. Decide if it was for selfish reasons or not, and tell them if they found out about it."

What if after William lost his wife in moments of desperation he sought out mediums and the like with the hope he would be able to communicate with her. He never got into contact with Cassidy, because few people know she can see ghosts and spirits. But Cassidy may have found out he was looking for a connection and could have possibly slipped him a note with some sort of final message from his wife to give to William. Without him ever learning it was Cassidy who delivered it.

How does that sound?