The agency had carried out detailed search in Kashmir even though it was alleged that Rana and Johar were Pakistani terrorists who had infiltrated in India.
The search met a dead end in the state as the agency could not gather any tangible evidence on their identity, CBI sources said.
CBI spokesperson said that a Letters Rogatory has been sent to Pakistan to gather any information available on Rana and Johar who killed with Ishrat and Javed Pillai in what was alleged to be a fake encounter in 2004.
CBI had promised a cash reward for anyone giving information about them.
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Gujarat Police had claimed in its FIR that Johar and Rana were actually Pakistani citizens who had come to India to eliminate VIPs of the state.
CBI, which is probing the case, has been able to get detailed information about Ishrat and Javed as it included the statements of their relatives and people known to them in the charge sheet filed on July 3.
CBI is likely to file a supplementary charge sheet in the case once it is able to unravel the conspiracy which led to the encounter.