The Central Bureau of Investigation (CBI) has asked Trinamool Congress lawmaker Derek O'Brien to appear before it next month in connection with the Rs. 10,000-crore Saradha chit fund scam. "We are probing certain transactions recorded in the bank accounts of the party's mouthpiece, Jago Bangla. That's why Derek O'Brien has been asked to join the investigation and provide clarifications," a senior CBI official told NDTV, adding that he has been instructed to come to the CBI's Kolkata office in the first week of August.