Singh, an SP-rank officer who has been coming to the NIA headquarters for last fortnight, was subjected to several rounds of questioning besides scientific tests including lie-detector test.
Searches at various places against him including his native place in Amritsar yielded nothing and documents recovered showed nothing incriminating against him, official sources said.
The NIA was trying to ascertain whether he had any role in the drug racket being run in the bordering districts of Pathankot and Gurdaspur.
On the intervening night of December 31 and January one, Singh was kidnapped along with his jeweller friend Rajesh Verma and cook Madan Gopal by Pakistani terrorists who later attacked the Pathankot Air base.

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