New Delhi: CBI Joint Director Rajiv Singh , who is overseeing a probe into the USD 2 billion PNB scam allegedly involving diamantaires Nirav Modi and Mehul Choksi , has been prematurely repatriated to his home cadre of Tripura.The move comes as the agency is planning to file for a Red Corner Notice against Modi and his uncle, Choksi.Three other officers of the CBI -- Joint Director (STF) and Special Crime Nina Singh, DIG Anish Prasad and Superintendent of Police R Gopala Krishna Rao -- have also been repatriated to their respective cadres.While Nina Singh is an IPS officer of the 1989 batch from Rajasthan cadre, the remaining three IPS officers are of Tripura cadre.Rajiv Singh is of 1993 batch, Prasad of 2003 batch and Rao of 2005 batch, a DOPT order issued on May 23 said.According to the order, Nina Singh, Rajiv Singh and R Gopala Krishna Rao will have to immediately return to their cadre and Prasad will have to return on June 2."Consequent upon the request of the respective state governments for premature repatriation of the officers, the competent authority has approved the repatriation/curtailment of tenure of the...officers working in the CBI," it said.