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BOULDER, Colo. (KDVR) — Boulder police (BPD) and University of Colorado Boulder police say that several suspicious letters and audio recordings left at Greek life homes were part of a scavenger hunt.

The items were discovered early Monday morning, and surveillance video showed someone walking up to the door to one of the homes, taping the letter to the door and then walking away.

BPD said it received at least five reports of an unknown person taping a white envelope to the front doors of both sorority and fraternity houses around 1:30 a.m.

Inside each envelope was a disc that contained audio, some of which included audio from the Criminal Minds TV show, according to BPD.

BPD said the people involved contacted police to let them know what was happening after concerns grew about the contents of the letters.

There will not be any criminal charges filed as part of this investigation.