A longtime Philadelphia police officer has been arrested on allegations that he sexually assaulted a teenage girl, starting when she was in the eighth grade.

Officer Charles Young was arrested Thursday on charges that include involuntary deviate sexual intercourse, corruption of a minor, and indecent sexual assault, all felonies. He is the fourth officer in three weeks to face criminal charges.

Young, 50, a member of the department for 21 years, retired before he was charged, according to a law enforcement source. The Police Department made no announcement about the charges. Other Philadelphia officers have retired before or after their arrest in an effort to begin collecting their pension payments.

The alleged victim in Young’s case said she first met Young and his partner in 2004 during her walks home from school, according to court documents. She was 14 at the time.

While on solo patrol one day, Young allegedly gave the girl his phone number and they met up that evening. They drove to Delaware Avenue and Spring Garden Street and engaged in sexual contact in his Cadillac, including intercourse, after Young allayed her concerns about the alleged assault, according to the arrest report.

“He asked her to trust him,” the report states.

Over the next four years, Young would allegedly pick up the girl from her home and school, sometimes in his police vehicle, and continued the sexual contact, giving her money on occasion and telling her not to disclose to her mother what had happened.

In January 2020, the victim identified Young in a photo array. She has provided other information that Internal Affairs investigators used to corroborate her allegations. Her name has not been disclosed, but she is expected to testify, if needed.

Young’s arrest last week follows the recent arrests of three other officers, all of whom Police Commissioner Danielle Outlaw publicly suspended for 30 days with the intent to dismiss.

Officer Gregory Campbell, 27, was arrested last week for allegedly crashing his car into a house in Northeast Philadelphia while intoxicated, breaking a woman’s legs, injuring her husband, and killing their dog.

The week before, Officer Admad Abduali, 32, was arrested for allegedly violating a protection-from-abuse order.

On Jan. 22, Officer Rahim Montgomery, 40, was arrested on charges of sexually assaulting a minor.

At least three other former Philadelphia police officers have open cases on allegations that include sexual assault, statutory rape, and possession of child pornography.

Young could not immediately be reached for comment Tuesday. His attorney, Jonathon Luff Jr., said Young denies the allegations.

“Obviously, he is innocent until proven guilty,” Luff said. “He is looking forward to fighting the charges and clearing his name.”

District Attorney Larry Krasner later said in a statement Tuesday afternoon that his office would “do everything in our authority to seek justice on behalf of the Commonwealth, support the victim in this matter, and to hold former Philadelphia Police Officer Charles Young accountable for his crimes.”

Staff writers Barbara Laker and David Gambacorta contributed to this article.