As per court order he was present when Sen was interrogated, Samir Das, Sen's lawyer said.
Sen, along with Ponzi scheme director Debjani Mukherjee and company official Arvind Singh Chouhan have been remanded to police custody for 14 days.
Chouhan, who has been kept in a separate place, is also cooperating with investigators during the interrogation," K Kanan, Assistant Commissioner of Police, Bidhannagar city police told PTI.
However, what surfaced during the investigation was not disclosed by the police.
Thousands of investors of the chit fund group have hit roads alleging they have been duped of around Rs 4,000 crore and hundreds of agents of the company have been rendered jobless.