QUETTA - Unidentified armed men gunned down a Sub-Inspector (SI) of Police and escaped from the scene of the crime.  Police said that unknown armed men sprayed bullets at SI of police in Nawan Kaley area of the provincial capital Quetta injuring him critically and escaped after committing the crime. The injured police official was rushed to hospital where he succumbed to injuries.  The police cordoned off the area after the attack and launched operation for the attackers.