William recognizes Mike by his last name, deliberately says that he killed his brother, and also the phrase " Symmetry, my friend." He clearly has some personal motive in the case of the Schmidts.
I personally have my theory that just like in the games, William is Mike’s dad in the movies, except Mrs. Schmidt was cheating on Mr. Schmidt (Mike’s supposed dad) when mike was born, but after he was born, Mrs. Schmidt said it wasn’t going to work out. But instead of killing Mike at that time, as he still had some sort of connection to Mike, being his biological father, he waited, and then, seeing the Schmidts had another child, decided to plan his revenge.
