By Jennifer McRae

BOULDER, Colo. (CBS4) – The Boulder Police Department says their investigation into white envelopes taped to the front doors of 6 sorority and fraternity houses at the University of Colorado reveals it was part of a scavenger hunt. Investigators said each envelope contained a CD with audio from the Criminal Minds television show about burning down a house.

(credit: Boulder Police Department)

Police said the envelopes were taped to the doors around 1:30 a.m. on Monday.

READ MORE: 'I Just Want My Dog Back': Reward Offered For Stolen Dog & Car In Westminster

(credit: Boulder Police Department)

When police released security video, those involved came forward and identified themselves to police. Officers said at this point, no criminal activity is suspected.

READ MORE: Palisade Orchard Has Frost Alarms Set To Watch Over Peach Crop During Arctic Blast

“There were several students’ parents concerned that their safety was in danger. We got a lot of messages last night so we were glad we able to put out information to determine what was going on to allay their fears. People were quite scared last night,” said Boulder Police Department spokesperson Dionne Waugh.

MORE NEWS: Worker Installing Sewage Line Killed After Trench Collapses, Trapping Man in Rising Water

(credit: Boulder Police Department)

The houses that received the envelopes include Chi Omega, Alpha Phi, Pi Phi, Kappa Alpha Theta, Alpha Sigma, Kappa Sigma.

Jennifer McRae