A four-year-old girl was sexually assaulted on Saturday and later thrown into a drain by rickshaw puller, police said. She is undergoing treatment while the rapist has been arrested.The incident happened in the Nai ki Mandi police station area, close to the Agra collectorate.Police said the man was caught in the act by another rickshaw puller who was relieving himself nearby, and ran for life after a crowd collected and chased him. He was caught, mercilessly beaten up and paraded naked before being handed over to police.Family members of the girl rescued her out of the drain and took her to the hospital. She had sustained a nasty head wound and injuries to her genitals.