COLUMBIA, Mo. -

A registered sex offender is now behind bars after walking into a Columbia elementary school.

Mark Salisbury was on parole for statutory sodomy when he walked a young girl into her classroom at Shepard Elementary School.

The principal of the school, Jacquie Ward, says the teamwork of school officials and local law enforcement officers as well as safety equipment in the school helped catch Salisbury.

Ward says these types of emergency situations are exactly why teachers and students practice drills and have cameras, intercoms and emergency buttons.

She claims she hasn't had a situation like this in her 17 years of education, but she feels prepared if they do arise.

She says, "We value the safety of the students and we'll do whatever it takes to protect them."