Kumar, who met ED authorities, was grilled for about 3-4 hours about various aspects of the finances and operations of the TV channel and his business associations, sources said.
Kumar also recorded his statement under the provisions of the Prevention of Money Laundering Act (PMLA), they said.
ED investigators also questioned and recorded the statements of few official representatives sent by DMK MP Kanimozhi on her behalf.
The representatives included financial advisors and accountants, they said.
Kanimozhi, on April 26, had submitted a set of financial documents to the ED authorities who are probing her role in the alleged financial irregularities in the 2G case.
The DMK Rajya Sabha MP, who is attending the current Parliament session, will be questioned soon.
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She was last year released on bail in the 2G case.
Kanimozhi and others have been charged by the CBI in connection with the channelling of Rs 200 crore to DMK family-run Kalaignar TV through a circuitous route.
The ED had summoned her for questioning about the transfer of the Rs 200 crore to the TV channel, in which she and Sharad Kumar hold 20 per cent stake each.
Some other transactions are also under the scanner of the ED in the 2G scam.
The ED, according to the sources, had earlier scrutinised documents related to the DMK MP's income, properties and personal investments and plans to take the probe forward, they said.
The ED had earlier initiated attachment proceedings under the Prevention of Money Laundering Act (PMLA) against other individuals and certain telecom firms involved in the case.
Besides the cases of Kanimozhi and Kumar, similar probe is underway under the provisions of the anti-money laundering Act against Swan Telecom promoter Shahid Usman Balwa's cousin Asif Balwa, Director of Kusegaon Fruits and Vegetables Pvt Ltd Rajeev Agarwal and Karim Murani of Cineyug Films (Pvt) Ltd. PTI NES