A 67-year-old  instructional aide at a Chester County high school was charged Friday with committing repeated sexual assaults on an underage female student, prosecutors said.

Arthur E. Phillips, who has worked for at Conestoga High School in Tredyffrin since 2006, was charged with multiple counts of institutional sexual assault, aggravated indecent assault without consent, aggravated indecent assault against a victim under the age 16, and related offenses.

Phillips, of Wayne, was being held Friday at the Chester County Prison in lieu of $500,000 bail.

In a letter to the families of students, Tredyffrin/Easttown School District administrators said Phillips had been suspended pending termination.

"We cannot adequately express our shock and dismay upon learning an adult responsible for the care of our students has been charged with such a deplorable act," Richard Gusick, district superintendent, and Amy Meisinger, principal at Conestoga, wrote in the letter.

"We have no information to indicate the employee was inappropriately involved with other students," they wrote, but nevertheless encouraged anyone with relevant information to contact Tredyffrin police.

Conestoga officials contacted Tredyffrin police Tuesday with information about an alleged sexual relationship between the student and Phillips, who worked in the television production studio at the high school, police said.

The girl befriended Phillips in 2016, and they had sexual intercourse on more than 10 occasions from January until this month, police said. On other occasions he would molest her, police said.

She told police she repeatedly told Phillips she did not want to have sexual contact but he forced her. She had not reached her 16th birthday when the assaults began.

Investigators said they found several hundred communications of a sexual nature between Phillips and the student on her two phones, and recovered photos, including one allegedly of Phillips' penis.

Police said that once the relationship came to light, Phillips crashed his car. Found in his car was a note that read: "I was just a guy trying to help a kid and boundaries just got gray."