NEW DELHI: Two of the six terrorists killed by security forces at the Pathankot airbase could have been “insiders”, top officials of the National Investigation Agency ( NIA ) told ET. These officials did not want to be identified.The forensic report due next week, examination of call logs of phones recovered from the attack sites in the airbase and a close scrutiny of personnel at the air force station will help determine the identity of the “insiders”, NIA officials said.Government statements after the January 2-3 terrorist strike on the Pathankot airbase had mentioned six intruders, but only four of them were identified as having been outsiders who crossed the Punjab border with Pakistan.NIA officials said the possibility that two of those killed by security forces could be insiders is strengthened by the recovery of only four AK-47 guns. These were used by four Jaish-e-Mohammad ( JeM ) terrorists. The black corner notice to be issued by Interpol is also against only four suspects killed by Indian forces.NIA officials said that to establish the identity of the two insiders they were looking at all personnel present at the airbase, as well as locals. There were around 3,500 people, including family members of those employed, at the Pathankot airbase during the attack.Close scrutiny is on to identify the two people who may not be JEM terrorists. Clearer answers will be available after the agency receives the forensic report next week. The Central Forensic Science Laboratory is preparing the forensic report. NIA officials said the report will also help nail the exact number of attackers. NIA Director-General Sharad Kumar told ET, “So far, we have recovered only four weapons and forensic reports of samples are awaited.”NIA has collected these samples from the debris of the airbase building that was blasted to kill two suspected terrorists. The agency also established that the four militants entered the airbase on the morning of January 1 by scaling the 11 feet wall and cutting the concertina wire. Investigators say the JEM terrorists had booby-trapped the part of the airbase they were hiding in. The call by one of the terrorists to his mother in Pakistan was made from inside the airbase.NIA officials also said the four terrorists inside the airbase may have panicked after the Indian Air Force conducted an aerial survey following an alert from Punjab Superintendent of Police Salwinder Singh . Singh had been abducted by the JEM terrorists on their way to the airbase, but he was let go before the terror group reached their target area.Salwinder underwent lie detection test on Tuesday and the procedure will continue on Wednesday. NIA D-G Kumar said: “He (Singh) has been interrogated many times. He is also a suspect. We are conducting a polygraph test on him.” There will also be other tests, including one that helps establish Singh’s personality profile.Polygraph tests will also likely be conducted on Singh’s cook Madan Gopal and the caretaker of the Somraj shrine, which is near the airbase. Salwinder’s jeweller friend Rajesh Verma will be interrogated immediately after he is discharged from hospital, NIA officials said.