Six children were slightly injured in the incident, which happened Friday at West Union Elementary School in Hillsboro, Ore., as a group of sixth-graders were outdoors having their class picture taken, The (Portland) Oregonian newspaper reported Monday.
The Oregonian said sheriff's investigators were treating the incident as a crime after discovering evidence of tampering. Authorities took photos and fingerprint impressions from the bleachers, which appeared to be missing some of its cross-support beams.
Washington County Sheriff's Office spokesman Sgt. David Thompson told the newspaper that if scrap metal thieves had removed the supports, they could be charged with assault, and if the collapse was the result of a prank, "It's pretty unconscionable. Luckily, no one was severely injured, but six kids did get hurt."
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