Pune police is investigating the persons behind circulation of doctored MMS about violence in Assam and Myanmar which trigged the recent attacks on north eastern students in the city.Cyber crime branch cell have arrested four persons on Tuesday and they have been remanded to police custody till Thursday. According to police, all of them are educated and computer savvy.Meanwhile, there is significant decline in the rush of north eastern people returning to their native places from Pune. The confidence building measures undertaken by police and local help groups as well as public representatives are having a positive impact on these people.