Because of where the crime happened I would place a connection to the Plackers over the Whittakers. However, you could also say that because the crime happened so close to the house, the suspect had no clue the girls were so close to home and therefore did not know them or the Placker family. I think the latter because it would be risky to kill to girls close to their house. Who knows though, what goes on in a murderers mind.
I agree and tend to think the killer came from the north and didn't even know that Taylor's house was so close. He might not have seen the mailbox in his fit of rage.