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Timeline of mailbox pipe bomb incidents:

Friday: Eight pipe bombs found in roadside mailboxes near Iowa towns of Eldridge, Farley, Asbury, Tipton and Anamosa and the Illinois towns of Mount Carroll, Morrison and Elizabeth. Six bombs explode, injuring four mail carriers and two residents.

Saturday: Six pipe bombs found in mailboxes near Nebraska towns of Dannebrog, Ohiowa, Davenport, Columbus, Scotia and Seward. None explode.

Sunday: Pipe bomb found in a mailbox near Albion, Neb.; it doesn't explode.

Monday: Pipe bombs found in mailboxes near Hastings, Neb.; Amarillo, Texas; and Salida, Colo.; none explodes.

Tuesday: FBI issues all-points bulletin for 21-year-old college student Luke J. Helder of Pine Island, Minn. Helder arrested outside Reno, Nev., and charged by federal prosecutors in Iowa with using an explosive to maliciously destroy property affecting interstate commerce and using a destructive device to commit a crime of violence.

Wednesday: The FBI says Helder confessed to making, placing the bombs. He is charged in Illinois with the same two counts as in Iowa and is charged in Nebraska with interstate transportation of explosives.