The development comes after the Madras High Court handed over the probe to the central agency in November last year rejecting the state CB-CID's plea for more time to crack the case.
The judge was critical of the CB-CID, saying it had been seeking adjournments without any progress in the investigation though five years had elapsed.
Ramajeyam, 50, was found murdered on the banks of Cauvery river in his home town Tiruchirappalli after he went for a morning walk on March 29, 2012.
He was found gagged and his hands and legs were tied.
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