The Kolkata police chief reached the CBI office at 10.20 a.m. and faced the interrogators for a little more than three hours before a lunch break.
Soon after Kumar returned to the CBI office at 3.15 p.m., CBI's investigating officer Chuzom Sherpa joined the interrogating team and interrogated him in connection with the Rs 17,520 crore Rose Valley chit fund scam.
"We are not authorised to speak about what the IPS officer (Kumar) and Ghosh said. Kumar was interrogated individually, first in connection with the Saradha case and then with the Rose Valley case before the accused (Ghosh) joined him in the evening," a CBI official, who wished not to be identified, said.
Ghosh, who was arrested in November 2013 in connection with the two chit fund scams and granted interim bail by the Calcutta High Court in 2016, said: "They (CBI) have summoned me. I have come here as per the Supreme court order and I will cooperate with them."
"The CBI is interrogating the very police officer who grilled me. This is my moral victory," he said.
Ghosh, a former Rajya Sabha member, had earlier implicated former Union Minister Mukul Roy, who has switched over from the Trinamool to the Bharatiya Janata Party, and 12 others in the Saradha chit fund scam.
On Saturday, the CBI interrogated Kumar for eight hours for "withholding and tampering important documents" in the scams.
Kumar arrived in Shillong on Friday evening from Kolkata via Guwahati after the Supreme Court, while hearing the matter on Tuesday, directed him to join the CBI probe at a "neutral place" in Shillong.
He was accompanied with three other senior state police officers - Additional Police Commissioner Javed Shamim, Special Task Force chief Murulidhar Sharma and CID chief Praveen Kumar Tripathi.