I'm not going to read every page but I believe its bill because he called out for a Sandy. I'm willing to bet Scratch is Sandy and he had a connection to her give up the tower. I'm also willing to bet that he was just going down stairs to possibly help the mallers get in and just died just as fast. As for motivation, he was willing to have Sandy to come up so far as to betray the tower to the mallers. My theory at least. Though, no evidence to support that but however improvable the answer the most likely it is. Or however way you say that super butchered sherlock holms quote.