A 15-year-old boy who turned himself in to police was charged Wednesday in the sexual assault of a 41-year-old woman on a Chicago Transit Authority Blue Line train earlier in the week.

Deshawn Isabelle was charged as an adult with one count of felony aggravated criminal sexual assault and one felony count of robbery, Cook County State's Attorney spokeswoman Sally Daly said.

An alert issued Tuesday by police said the 41-year-old woman got on an eastbound train at the Oak Park Avenue station a little after 3 p.m. Monday. Soon after, a male who got on the train at the Forest Park station attacked her from behind, police said.

He knocked her to the ground, sexually assaulted her, and then robbed her of her iPhone and cash, police said.

After the attack, he got off the train at Cicero. He then rode a westbound train to the Austin station, police said.