Everyone played a part in causing Susan's death, including Susan. Looked at it that way, you could say Ka was ultimately responsible. Roland and Susan knew it was dangerous. She was Thorin's gilly, and even though she really didn't want to go through with the deal, she and Cordelia had already accepted money and was bound by tradition. Very dangerous. Sheemie helped to facilitate Roland and Susan's liasons. Cuthbert tried to bring Roland to his senses, but ultimately left it up to Roland. Alain expressed his concerns but did nothing.

Everyone played their part, either through active participation or inaction.