Sources in the agency said the conspiracy angle behind the fake encounter needed to be further established so that a watertight case is made out.
CBI is looking into the role of Intelligence Bureau's Special Director Rajendra Kumar and others, a move which may intensify the bickering between two central agencies.
Despite the Union Home Ministry's contention that Kumar could not be prosecuted without its sanction, CBI officials said it did not require any sanction if there is evidence against him, an IPS officer of 1979 batch.
Kumar had been questioned by CBI at least thrice regarding his alleged role in the conspiracy to carry out the "fake" encounter in which 19-year-old Mumbra college student Ishrat Jahan and three others were killed nine years ago.
More From This Section
CBI sources said they have evidence indicating that Kumar was one of the officers who had interrogated Ishrat when she was allegedly taken into illegal custody by Gujarat Police before being killed in the encounter.
They said the officer was questioned at length with regard to the alleged interrogation and other inputs which suggest his role in the conspiracy leading to the encounter in which Ishrat was killed along with three others on June 15, 2004 by a team of Crime Branch officials on the outskirts of Ahmedabad.