Singh deposed at the CBI headquarters in the morning following summons for his cross-examination in the case along with the 'whistle blower' Samuel. Earlier, the CBI had questioned Samuel along with Singh's personal secretary.

Later, former TMC leader Mukul Roy also joined the probe. Roy left the CBI headquarters in the evening after two hours.

While leaving the headquarters, Roy, who joined the BJP in November 2017, said, "Yes, I went to the CBI office. The CBI did not call me. They didn't ask me anything about Narada sting."

Roy, the former aide of West Bengal Chief Minister and TMC chief Mamata Banerjee, had a fallout with her in 2015 when his name cropped up in the Saradha scam as well as the Narada sting operation. After he was suspended from the party for six years, Roy quit the TMC in September 2017.

Source said TMC MP Singh didn't appear before the CBI on July 29 citing personal reasons.

CBI had also summoned TMC MP Aparupa Poddar in connection with the Narada sting operation probe, sources said.

In 2016, Samuel, editor and Managing Director of Narada news portal, had just before the West Bengal Assembly elections broadcast a sting video, in which a number of TMC leaders were allegedly seen taking money on camera.

The purported video footage of the sting operation surfaced before the 2016 Assembly polls. The CBI lodged an FIR in April 2017 following a court order, naming 13 TMC leaders and have interrogated many of them. The purported footage was also sent for forensic examination.

The Enforcement Directorate is also probing the money trail in the case.