The mother of Deshawn Isabelle, 15, recognized him from surveillance photos after a robbery and sexual assault on a CTA Blue Line train. Realizing what her son had done, she marched him down to the police station to turn himself in.

On Thursday, prosecutors said that Isabelle grabbed the 41-year-old woman from behind and robbed her, additionally sticking his hand in her jeans and sexually penetrating her.

“The defendant continued to punch victim repeatedly about her head, face and body. Defenden repeatedly kicked victim and stomped on her while making monetary demands of the victim,” Joe DiBella, assistant state’s attorney, said.

Isabelle allegedly took the victim’s iPhone as well as $2,000 in cash that she was planning on wiring to her family in Thailand.

“Defendant indicated he used the money he took to spend on junk food, his high school graduation costs, and Air Jordan jumpsuits,” DiBella said.

Isabelle and the victim were the only two passengers in the train car at the time. The victim, according to police, was hospitalized overnight with a concussion.

After Isabelle’s mother saw his face on the surveillance photos, she took him down to the station to turn himself in, where he signed a written confession.