The incident occurred on a train travelling to London Victoria at around 3:10pm on August 5. A 15-year-old girl was seriously sexually assaulted by a man on board the service, before he left the train at Gatwick Airport station. A 19-year-old man has since been arrested on suspicion of Assault by Penetration, following an appeal by British Transport Police. He has been released on conditional police bail while enquiries continue.