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RENO, Nev. (AP) _ The FBI said Wednesday that 21-year-old college student Luke Helder had confessed to planting 18 pipe bombs in rural mailboxes in five states. Six people were injured in the spree.

Using a map, Helder pointed to towns where he placed eight bombs in Illinois and Iowa on Friday, FBI agent Mark Heavrin said in an affidavit.

Helder also described placing other bombs in Nebraska, Colorado and Texas during the weekend and admitted he made 16 more bombs in a room at a Nebraska motel near Omaha, Heavrin said.

The suspect's own father and an alert motorist led to the arrest Tuesday of Helder, of Pine Island, Minn., who majored in art at a university in Wisconsin and sang in a punk band called Apathy.

He was arrested after a high-speed chase along a desert highway and a cell phone conversation with an FBI negotiator and his parents.

Authorities put out an alert for Helder after his father, Cameron, called police late Monday about a letter from his son that contained reference to the bombings, authorities said.

When authorities pulled him over, Helder dropped a gun out his car window and was arrested without incident. At least one other gun was found in the car, and bomb squads were called to the scene along Interstate 80 some 50 miles east of Reno to dismantle five pipe bombs found in the car, said Highway Patrol Maj. Rick Bradley.

Four letter carriers and two residents were injured Friday by bombs left in mailboxes in Illinois and Iowa. The 12 other bombs found later in Iowa, Nebraska, Colorado and Texas did not explode.