Paint gun bandits broke into University High School in Normal early this morning vandalizing walls inside the building. School officials cancelled classes so workers could clean up the mess.

Authorities suspect it was part of a senior prank. Illinois State University officials say paint gun bandits sprayed paint pellets on the walls of the first and lower floors.

Spokesman Jay Groves said, "It was bad enough that we had to cancel school and the big problem is that paintball is a vegetable based substance, it's very slippery, so we didn't want any kind of a safety hazard for the students, faculty or staff members."

Groves says the paint bandits did not touch any of the classrooms.

ISU campus police say there were no signs of forced entry and they believe more than one person may have been involved in what they suspect was a senior prank.

The Police Department's Nichol Bleichner said, "I think it was made to look like a senior prank. Nothing on the senior floors were touched. It was mostly on the freshman side, cafeteria, sophomore area and around the office."

"A lot of people use the word senior prank but no one in school today is laughing because obviously it's cost the students a day of class, it's cost our facilities planning folks lots of work to get it cleaned up. It's taking time away from what the school should be used for."

Friday was the last day for seniors at the school...and despite the interruption for everyone else Principal Jeff Hill says students will wrap up the school year this week.

Anyone with information on the incident is asked to call ISU police at 309-438-8631.