Walworth County bus driver accused of sexually assaulting young girls

WALWORTH COUNTY, Wis. (CBS 58) -- A 39-year-old Walworth County bus driver is accused of sexually assaulting young girls who rode his bus. 

Matthew Gribben has been charged with the following: 

• First degree child sexual assault (4 counts) 
• Exposing a child to harmful material (2 counts) 

According to a criminal complaint, Gribben -- who is a school bus driver who transports children from their homes to school in Walworth County -- admitted to engaging in inappropriate behavior with children. 

Gribben allegedly told investigators, when he transported the children he would occasionally touch some of the female students on their backside, and there were two students he showed pornography to. 

During another incident, the complaint says he exposed himself to a female child. 

The criminal complaint says the victims range in age from 8-11. 

Investigators say Gribben admitted to touching other girls on the bus but could not remember their names. 

In court on June 29, a judge set bond for Gribben at $150,000. 

He's due back in court July 13.