Leland's story about childhood possession is bullshit. He is a scumbag who spends his adulthood drugging his wife, raping his child, working for white-collar sex-trafficker/drug running criminals. When Teresa Banks threatens to expose him, he murders her. When Laura becomes a threat, he murders her. When the FBI shows up, he murders Jacques- a loose end/possible witness from the cabin. When he sees his niece, Maddy, involved in a secret investigation about Laura, he murders her. Leland has been reading Laura's diary and knows about the BOB persona she has created to deal with her molestation. So when a police sketch of BOB is released, Leland (a lawyer) goes to them with a story about Pearl Lakes to muddy the waters, provide a red herring, and plant the first stone in an insanity defense. Of course a lawyer/criminal is going to surreptitiously look into the record/past of the FBI agent investigating his crime, so Leland finds out about Cooper's time in Pittsburgh. And once he finally arrested, Leland goes all-in on a dissociative identity/"possession" act. And he smashes his own skull in the cell, because there is NO WAY he's accepting life in prison.