PATHANAMTHITTA: An RPF officer was beaten up by a group of youngsters for questioning them over ganja use. Head constable Shantharao of the Chengannur unit got injured in the attack. The Thiruvalla police arrested Thiruvalla natives Libin, Sreejith and Alappuzha native Aji in the incident. The police said that the accused belonged to the ganja mafia group. The accused were provoked when Shantarao stopped and questioned them for using ganja on the station premises. They will be handed over to the Railway Police immediately.