MINNEAPOLIS (WCCO) – A sex offender who was arrested after he was found sitting on a St. Paul school bus has entered a guilty plea for violating his predatory offender registration requirements.

Michael Charles Friedrichs, 61, entered a guilty plea for violating his registration requirements in Scott County, which is where he was living. He will be sentenced July 29.

According to authorities, officers responded to Chelsea Heights Elementary School Feb. 28 for a report of an unauthorized man on a school bus. Police arrested Friedrichs for violating his sex offender registration. The students were returning from a field trip to the Walker Art Museum when Friedrichs was found on the bus.

RELATED: ‘We Had No Idea How He Got On’: Sex Offender Michael Friedrichs Sneaks Onto St. Paul School Bus

His previous crimes include engaging in sexual activity with two 15-year-old boys, as well as exposing himself to elementary school children on a Minneapolis school bus in 2011.

The bus driver immediately called police when Friedrichs was found sitting in the back, according to a statement from St. Paul Public Schools. Police say he told officers he had been at the Walker and boarded the wrong bus.

School officials told parents how they believe Friedrichs got on the bus.

“The school told us the footage from the camera shows him prying open the doors at some previous location prior to getting to the Walker when the bus driver was off the bus,” said Maggie Zimmerman, a chaperone.

Friedrichs is currently in custody.