"The NIA sleuths arrived this morning and they have been questioningSardana at Ribander office of crime branch," a senior ATS official said. Sardana's father was reported to be an ex-Major General from Dehradun.
Sardana was arrested yesterday on suspicion, after he was found loitering at Vasco Railway station with five passports and a laptop.
The ATS, which managed to crack the password of his laptop and access the emails and documents, said he was gathering information about bomb blasts which have taken place across the country in the past.
Sardana, a 44-year-old chartered accountant, was booked under section 41 of the CrPC which deals with preventive arrest.
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He was living in a railway dormitory, 35 km from here, since January 22 and had been extending his stay, the official said.
Sardana is based in Mumbai and has worked for MNC firms like Accenture with postings in Hong Kong, Malaysia and Saudi Arabia, the official said.
Goa Police are on alert after a letter purportedly written by ISIS, threatening to kill Prime Minister Narendra Modi and Defence Minister Manohar Parrikar, was received on January 13 by the state secretariat, which was handed over to the ATS.
Police had detained a Syrian, a Nigerian and a Yemeni last week for overstaying and they were probed from the terror angle.