a 15-year-old boy has been arrested for allegedly robbing , beating and sexually assaulting a woman on a chicago train after his mother recognized his face on released surveillance images and turned him in to police .
deshawn isabelle punched the 41-year-old woman in the head from behind and then dragged her to the ground by pulling on her hair before continuing to punch her in the head and face as she crouched in the fetal position .
the middle school student was sitting in the otherwise empty carriage when the woman boarded the cta train in oak park on monday at 3 pm .