Why going public about the alert? What the Police commissioner is trying to achieve with this? Instead of combing operations and catching the culprits before they execute their plans, Delhi police seems to warn the terrorists that they are in the know of their sinister plan and thereby either giving time to the terrorists to reorganise their plans or divert them to some other nearby town to execute their plans.
Most likely this approach seems like postponing the threat by some more weeks/months and saving the Delhi citizens. This is an approach nevertheless, but indicates the level of desperation of Indian security agencies. A similar thing happened a few weeks ago in Bombay too! They have released the sketches of possible terrorists and that seems Bombay polices way of shooing the terrorists away for a while informing them that the Police is aware of their threat.
