Two teenagers who planted explosives in three mailboxes here found instructions to make them on the Internet, police said.

Cedar Falls police Officer Mike Haislet said the explosives consisted of black gunpowder wrapped in paper. You "put a fuse in it and light it and run," he said.

"They didn't actually blow up the mailboxes," he added. "They just exploded inside the mailboxes."

Michael Andrew Truelson, 629 Stanwood Drive, and Casey Joseph Schwickerath, 2222 Linwood Drive, both 15, were charged Friday with reckless use of explosives, a serious misdemeanor. They also will face federal charges because mailboxes were the targets of the explosives.

Haislet said the teens found the instructions on You Tube. The 2-minute, 22-second posting shows viewers "how to make a simple yet effective cracker" alternating between written instructions and photos to a soundtrack of the rock band AC/DC's "Back in Black." It ends with a brief video of the bomb exploding in a yard.

Cedar Falls police investigated the bombings after a homeowner at 836 Maucker Road reported a fire in a mailbox late Wednesday night. During the investigation, police also found other mailboxes damaged by homemade explosives at 803 Stanwood Drive and 3917 Southlawn Drive.

One of the homeowners, who didn't want his name used, said they discovered the homemade bomb sometime after the explosion. His wife noticed the mailbox was open "and it looked like someone had burned some paper." The post office advised them to contact police.