They said the investigating officer (IO) of the case recorded Karti Chidambaram's statement under the Prevention of Money Laundering Act (PMLA).
Karti Chidambaram was first grilled at the central probe agency's office here on April 10 for about ten hours in connection with the case.
He has been summoned for questioning next week.
The case relates to the Foreign Investment Promotion Board (FIPB) approval granted in 2006 by his father.
The Supreme Court had on March 12 directed investigating agencies, the CBI and the ED, to complete their probe into the 2G spectrum allocation cases, including the Aircel Maxis alleged money laundering case, in six months.
The agency had said FIPB approval in the Aircel-Maxis FDI case was granted in March 2006 by Karti Chidambaram even though he was competent to accord approval on project proposals only up to Rs 600 crore and beyond that it required the approval of the Cabinet Committee on Economic Affairs (CCEA).
The ED is probing "the circumstances of the FIPB approval granted (in 2006) by the then finance minister", the official said.
"However, approval was not obtained from the CCEA," it had alleged.
The agency said its probe revealed that the case of the said FDI was "wrongly projected as an investment of Rs 180 crore so that it need not be sent to the CCEA to avoid a detailed scrutiny".
The ED is probing the Aircel-Maxis deal under the PMLA after taking cognisance of a 2011 CBI FIR in the case.
Karti Chidambaram's father, former minister P Chidambaram had earlier described the ED action in this case as a "crazy mixture of falsehoods and conjectures" and said that the charge sheet filed by probe agencies had been rejected by the court.
However, the agencies have maintained that the FIR in the case has not been quashed.
In September last year, the ED had attached assets worth Rs 1.16 crore of Karti Chidambaram and a firm allegedly linked to him in connection with this case.
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