In short, the life of Arjun Singh is being made easy by Maya who has been given a "Mantra" by Sonia since both are sisters - in - arms now. Lest there is a public uproar if he is let of the hook (which is going to be the ultimate outcome), the case is being handed to CBI just to create an atmosphere of Inquiry. Finally, he will be acquitted as "Not - Guilty."
What else, then, is the logical conclusion of giving the case to CBI? It is the Congress's "Yes - Man" after all.