DENVER -- Last week, a duffel bag containing a Kermit the Frog doll caused a scare at Peak to Peak Charter school.

The prank involving four male students ages 14 to 16, started a couple of months ago in a high school classroom, Lafayette Police Cmdr. Mark Battersby told the Boulder Daily Camera newspaper.

Battersby said the teens kidnapped the doll from a teacher and traded it back and forth for weeks. At one point the teens reportedly put fake blood on the doll with a red Sharpie pen.

The newspaper reported that last week, one of the teens threw a gym bag with the doll inside in a student's pickup truck and that student didn't want it, so he told his brother to take it out and leave it in the parking lot so another teen could come pick it up again.

That student never came back to get the bag, Battersby said, and it sat in the parking lot overnight.

"That's what caused the commotion," he said.

Wednesday morning, a school employee spotted a duffle-type bag in the parking lot and because it was suspicious, police were called. The bomb squad sent in a robot to check out the bag and inside they found the doll.

Students who were already at the school were kept inside during the incident. After the all-clear was given, the students were sent home and classes were canceled for the day.

Lafayette police are not pursuing charges against the teenagers who were involved because they didn't mean any harm, Battersby said. The school may still discipline the students.