Since the first death there is a problem in conflict with her husband, but she can't move and thus forcing Benson partnered to murder because Benson knows the area in the House as well.
Before dying because their conflict with her husband, but she can not move easily, thus forcing Benson Benson collaborated to murder because the space in the house as well.
Due to a conflict with her husband before she can't move convenient and therefore forced to Benson cooperate to murder because Benson know the area in the house as well.