Punjab Police officer Salwinder Singh, who is alleged to be involved in Pathankot Air Base attack, used to speak with drug smugglers active in that region often.
NIA source has revealed that many numbers from Salwinder Singh's call history belong to drug smugglers.
On Tuesday, the NIA had asked mobile telephone service providers to submit details about the calls made using three particular towers which give coverage to the IAF base in Pathankot, after initial probe indicated that the terrorists had entered the restricted area in the morning of January one, sources said.
They said officials of Defence Security Corps and others responsible for handling entry and exit at the base were being questioned to ascertain possible lapses that allowed the terrorists to enter the restricted areas without being noticed.
Meanwhile, Security agency has also blamed that Salwinder Singh is changing his statements quite often.
NIA has also summoned Somraj, caretaker of Panj Peer Dargah in Punjab, which Singh had claimed to have visited before he was kidnapped by terrorists, who attacked the Pathankot Air Force base hours later.
The shrine is located a few kilometres from Bamiyal, the village from where the terrorists were suspected to have infiltrated India before mounting the attack.
(with PTI inputs)