According to M. William Phelps, author of "The Devil's Rooming House", investigation appeared to show that Amy was buying the arsenic to kill large numbers of rats. However, it appears that she did not buy all of the arsenic which killed her patients. The doctor and some of the patients had signed off to purchase it. The investigation pursued Dr. King because more evidence was piling up against him, but suspicions were focused back on Amy when someone suggested to clearly check all records of arsenic purchases.