CBI sources said the forensic experts carried out detailed ballistic examination of fire-arms seized by the agency and the crime scene to understand which among the weapons could have been used during the crime.
The team also took biological samples from the site of the crime and also analysed the place exhaustively in the presence of the two arrested accused--Sanjeev Pratap Singh alias Guddu Singh and Rajeev Pratap alias Raju Singh, they said.
The CBI is probing killing of DSP Zia-ul-Haq, village head Nanhe Yadav and his brother Suresh in Balipur village on March two and registered four FIRs in this connection.
The agency also grilled Yogendra Yadav alias Babloo, son of killed village head Nanhe Yadav, for several hours in connection with the killings as he was alleged to be present on the site when the murders took place.
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District magistrate Vidya Bhushan said the administration has deposited 14 licenced fire-arms from Balipur village.
The probe is being supervised by two senior officers of the CBI including Joint Director R S Bhatti and DIG Anurag Garg who are known for the good record in tackling special crime cases.