SPOKANE, Wash. (AP) — Serial killer Joseph Edward Duncan III died in federal prison recently, having admitted to killing seven people, including five children, in Idaho, Washington state, Montana and California. Some question whether Duncan killed even more people. Following his arrest in 2005 for the slayings of four members of an Idaho family, federal authorities reviewed missing children cases nationwide. The assistant U.S. attorney who prosecuted him in Idaho believes all of Duncan’s killings were revealed in court. The 58-year-old died Sunday at a hospital in Indiana near the federal prison where he was on death row. The native of Tacoma, Washington, had recently been diagnosed with terminal brain cancer.