The National Investigation Agency, NIA, has summoned Gurdaspur SP Salwinder Singh to New Delhi on Monday for questioning in connection with the ongoing investigation into Pathankot airbase terror attack case. Singh was abducted while riding a personal vehicle which was hijacked and later used by the terrorists on the night of 31st of last month.<br/><br/>Four NIA teams are camping in Punjab to verify the facts and examine witnesses in close cooperation with the state police. All the arms and ammunitions used by the terrorists in the attack and other articles found on their bodies and from the crime scene have been seized. Search of the Air force station campus is being conducted to recover any trace evidence left behind by the terrorists. <br/><br/>DNA samples collected from the vehicles used by the terrorists are being sent for forensic examination. Footprints suspected to be of the terrorists have also been lifted by forensic experts and have been sent to Central Forensic Science Laboratory. Post-mortem of the bodies of terrorists was conducted at Pathankot Civil hospital yesterday and their body tissues were preserved for DNA sampling.