CBI sources said Samuel is not an accused and the motive was to get information about the sting and circumstances in which it was done.
After coming out from questioning by the CBI, Samuel told reporters that the team asked about the planning of the sting, circumstances in which money was purportedly given, and the location of exchange, among other details about the sting.
He said he was allowed only one break during the five-hour-long interaction.
The preliminary enquiry (PE) has been registered following the directions of a division bench of the Calcutta High Court, comprising of acting Chief Justice Nishita Mhatre and Justice T Chakraborti.
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The Narada sting tapes, which were released to different news organisations before the 2016 Assembly elections in West Bengal, showed people resembling senior TMC leaders receiving money allegedly for giving future favours.
The Calcutta High Court had on March 17 ordered the CBI to conduct a preliminary probe into the Narada sting operation in which the TMC leaders were allegedly seen taking money.
The Supreme Court had extended the time given to the CBI for registration of the FIR in the case from 72 hours to one month.