Updated at 11:55 a.m.

A bus driver for the Tigard-Tualatin School District is accused of sexually abusing a developmentally disabled child on his school bus, Tigard police said Thursday.

Mario Mendez Ruiz

The student told school district officials that Mario Mendez Ruiz, 60, had been abusing her since late March, Tigard police spokesman Jim Wolf said. Mendez Ruiz is a special needs bus driver for the school district.

In two cases, he drove the school bus from its usual route after all the other students had gotten off the bus, and parked in a nearby neighborhood, where he abused the girl, Wolf said. He gave the student money and told her not to tell anyone about the abuse, police said.

Mendez Ruiz has been on paid administrative leave since the district learned of the allegations.

Police are not aware of any other alleged victims.

Tigard-Tualatin school district spokeswoman Susan Stark Haydon said Mendez Ruiz has worked for the district for two years. He passed a fingerprint and background test before he was hired, she said.

"This is disturbing to us on many levels," Stark Haydon said in a statement. "We are extremely concerned for the student and very troubled that the person accused of harming her was an employee."

The district set up the student with a school counselor, Stark Haydon said. The district has also provided her access to an outside counselor.

Mendez Ruiz was indicted by a Washington County grand jury on April 21 on charges related to the sexual abuse of a child. He faces charges of second degree kidnapping, third degree sexual abuse and first degree criminal mistreatment, court records show.

Mendez Ruiz was arrested on Wednesday. He is currently lodged in the Washington County Jail. His bail is set at $50,000, jail records show.

This post was updated to include a statement from the school district.

-- Samantha Matsumoto

503-294-4001; @SMatsumoto55