The Uttar Pradesh police are investigating a letter reportedly written by the officer who led a failed raid on notorious gangster Vikas Dubey on Friday and was killed along with seven other cops. A top officer has asked for a thorough inquiry into the letter, which, if found and verified, could be damning evidence of policemen helping the criminal. Vikas Dubey, allegedly tipped off about the raid by an insider in the police, is missing since the massacre of cops.