The three-train tragedy in Odisha's Balasore, which left 275 dead and around 1,000 injured, will be investigated by the CBI as only a detailed probe can establish criminal tampering, if any, with the point machine or the electronic interlocking system. The Congress has hit out over the CBI probing the case. But as the political blame game continues, there is still one question - who is responsible for the Odisha train tragedy?