What makes Harper and Miles give the FBI an anonymous tip about the donor registries? What do they find?

Another hunch of Drewe's prompts Harper and Miles to send the FBI another tip anonymously via computer. She believes that there could be additional victims listed on donor registries. The FBI finds two kidnappings, including Peter Levy. The killer made a reference to "Levy" in one of his letters, so it is reasonable to think that the killer does have Peter Levy.