This is the first time that the ED has questioned Raja in the case.
During questioning, ED investigators grilled Raja on various issues related to spectrum allocation under his ministership and also about his personal finances, sources said.
Raja, according to sources, was also questioned about his Ministry associates and their role in the grant of telecom licences.
The ED also took possession of financial documents that it had asked Raja to bring along with him for questioning, under provisions of the Prevention of Money Laundering Act (PMLA).
Sources said the former DMK minister could again be called for questioning with regard to the policy decisions taken to grant spectrum to few specific firms.
Raja had got bail in May this year after he was arrested by the CBI last year in the same case.
