CEDAR PARK, Texas (KXAN) – The Leander school bus driver who was fired this month after being accused of roughing up a 9-year-old aboard his vehicle was arrested Friday on a charge of injury to a child.

Helmut Derer, 67, was placed in custody after an investigation showed he shoved the boy into his seat and “used his knee to strike the child’s leg.”

The Leander school district has fired Derer, an eight-year district employee, after the incident was reported..

The boy from Charlotte Cox Elementary who was riding the bus home with his 11-year-old sister Wednesday afternoon. According the boy’s mother, who said she has viewed the school bus surveillance video, the two siblings were verbally fighting as the driver pulled up in front of their house.

the mother said the driver turned the engine off which turned off the surveillance cameras on the bus for a brief moment. When the video comes back on, the mom says her son was lying on his back on the seat. The bus driver grabbed her son by his shirt with both hands and started “shaking him with force.”

She said her son hit his head on the side of the bus and started screaming and crying. When her son asked the bus driver why he was doing that, she said the bus driver responded with “I can. I do it all the time.”