Hi,
I've actually thought more about this than I probably should have, but what else can you think about when folding laundry, etc?
There was a prophecy that had to be fulfilled so that the evil Mordred could come back. One person descended from Marcus had to fulfill that prophecy, and Samuel ended up being the one. He didn't know what he was doing because he was possessed by Mordred when he committed the acts, and he thought they were dreams. Mordred said he would "come back" and he did, through Samuel. Samuel had to kill five people to fulfill the curse, and release five souls. He killed William, the Gardener, Vick, the Doctor and Robert. Each time he killed someone, he placed the symbol next to their bodies. This means he killed William, and returned for the funeral (not remembering any of it). After William was killed, Robert would have searched his desk and found the ring and the letter to Samuel, as well as the new will cutting him out of the inheritance. He hid these out of greed; not because he was William's killer. We know that the butler realized at some point that Samuel was the killer and asked forgiveness for keeping it a secret during confession. He was the only one who knew until James found out. James found out when Samuel murdered Robert in front of him. James was captured by the police, told them he didn't kill Robert (the truth) and wrote Samuel's name on the wall probably with red paint (he had the paints there in his room). He then hung himself. He had told Samuel that he couldn't stand going back to the sanitorium, and so he committed suicide when they took him back. Samuel only knew the truth about himself at the end when he put the black hair and the dreams and the prophecy together.
Robert was conducting experiments on patients and killing them, probably because he was doubling up on the doses. He had a system set up so that he would have his gardener deliver the bodies (probably chopped up in the chopper after having been disguised as bags of leaves) to the doctor, who disposed of them. Those were murders that Robert committed, but not for the prophecy.
I thought it was odd that they threw in the information about Samuel's wife dying in the fire and Robert's wife leaving him (although he kept her photo), and yet they never really explained what happened. I thought they possibly just wanted an explanation for the fact that the old part of the house had been burned and was a ruin, so they invented the tragic story of Samuel's wife. It also served as an explanation as to why he had stayed away from the castle for such a long time. I don't think he killed her, although he may have blamed himself for having her live there with him or for not being able to save her. I also thought it was odd that they mentioned the nursery but we were never able to enter the room. I thought an old nursery would have been scary!
Happy gaming,
Beth