Three senior CBI officers questioned Kumar for nearly nine hours on Saturday about his alleged role in the tampering of crucial evidence in the scam, the officials said.
There was no briefing by the Central Bureau of Investigation (CBI) on the questioning which began at around 11 am at its highly secured office at Oakland here as per the directions of the Supreme Court.
Kumar's counsel Biswajit Deb, who is also the TMC coordinator for Meghalaya, said Kumar is "cooperating and complying" with the CBI.
"He (Kumar) has come here on the orders of the Supreme Court. He has complied earlier and he is complying now as per the orders," he told reporters outside the CBI office.
Kumar led the special investigation team (SIT) formed by West Bengal Chief Minister Mamata Banerjee to investigation the chit fund scam before the probe was handed over to the CBI by the apex court.
He will be present at the CBI office for the second day tomorrow, said Deb, who met Kumar along with two senior IPS officers from West Bengal -- Javed Shamim and Murlidhar Sharma -- thrice during the day for brief periods.
The agency may confront him with Kunal Ghosh who has also been called on Sunday, but a final call will be taken by the investigating officer present in Shillong, agency sources said.
The CBI is relying on a 91-page letter from Ghosh, who was expelled by TMC, to the Enforcement Directorate, detailing the role of Kumar in handling the ponzi scam probe after the main accused, Sudipta Sen and Debjani Mukherjee, both promoters of Saradha Group of companies, had fled to Kashmir, officials said in Kolkata.
Sen and Mukherjee were arrested in 2013 from Kashmir.
Ghosh had implicated BJP leader Mukul Roy, who was once the right-hand man of Banerjee and 12 others in the Saradha scam.
The Supreme Court had directed Kumar on Tuesday to appear before the CBI and "faithfully" cooperate in the investigation of cases arising out of the Saradha chit fund scam.
The apex court had also directed Kumar to appear before the investigating agency at a neutral place in Shillong "to avoid all unnecessary controversy" and made clear that he would not be arrested.
The CBI had moved the Supreme Court after its officials were thwarted by Kolkata Police when they had gone to Kumar's official residence in Kolkata to question him on February 3.
Chief Minister Mamata Banerjee had rushed to the spot and had staged a three-day 'Save the Constitution' dharna against the CBI move and accused Prime Minister Narendra Modi and BJP national president Amit Shah of plotting a 'coup'.
The central investigating agency had said that its officials had wanted to question Kumar to plug the holes in the Saradha investigation case as he was supposed to be in possession of certain key documents as a member of the special investigation team.