Singh, at present posted as Assistant Commandant of 75th Punjab Armed Police after being shunted out as Superintendent of Police (Headquarters) Gurdaspur, had agreed for a polygraph test after NIA informed a designated court about alleged "inconsistencies" in his statements before Punjab police and NIA.
He was being questioned by a team of experts from Central Forensic and Scientific Laboratory and the questioning will continue tomorrow, official sources said.
Eyebrows were raised when Singh said that he and the cook were released whereas one of their friends, who was travelling with them -- Rajesh Verma -- had been left bleeding midway by the terrorists.
"We are only looking for correct sequence of events so that the investigations can progress in right direction," a NIA official said.
More From This Section
Also his statement that he was returning from a shrine, which he often visited, was found to be allegedly incorrect after NIA questioned caretaker of the dargah Somraj who told the probe agency that the police officer had come for the first time.
So far four bodies of terrorists have been recovered while two others are believed to have been burnt in the building where they were holding for more than 10 hours.