What factors contribute to the suspicion that Cust in the killer in the novel, The A.B.C. Murders?

The novel is interspersed with chapters about Alexander Bonaparte Cust. In this way, it seems that the novel is setting him up to be the murderer, and it would almost seem like this is true - until the very end. At the beginning of the novel, the chapters about Cust show that he is in the places where the murders are taking place, he has a list of names, and many ABC Guides. All these factors point to the fact that he is likely the murderer.