His health collapsed within a day and he was dead by the evening. The official cause of death was gastric ulcer. His sister Nellie Pierce inherited his personal papers. She soon noted occasions where Archer-Gilligan was pressing Andrews for money. Archer-Gilligan's clients showed a pattern of dying not long after giving their caretaker large sums of money.
As the deaths continued, Pierce reported her suspicions to the local district attorney. He mostly ignored her. Pierce took her story to The Hartford Courant, a newspaper. On May 9, 1916, the first of several articles on the "Murder Factory" was published. A few months later, the police started seriously investigating the case. The investigation took almost a year to complete, but the results were interesting. The bodies of Gilligan, Andrews, and three other boarders were exhumed. All five had died of poisoning, either by arsenic or strychnine. Local merchants were able to testify that Archer-Gilligan had been purchasing large quantities of arsenic, supposedly to "kill rats". A look into Gilligan's will helped to establish that it was actually a forgery, written in Amy's handwriting.
According to M. William Phelps, author of the true crime The Devil's Rooming House, investigations appeared to show that Amy was buying the arsenic to kill off large quantities of rats. However, it appears that Amy did not buy all of the arsenic which killed her patients; the doctor as well as some of the patients signed off to purchase it. The investigation was pushed to pursue 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. Once evidence was found of Amy sending her own patients to the drugstore to buy quantities of arsenic, the police were able to arrest and convict Amy.
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