However, the Communist Party of India-Marxist kept alleging that the CBI was stalling the 'real investigation'.
Thus entered Prashant Bhushan, the senior Supreme Court lawyer and well-known activist, who has been appearing for the Centre for Public Interest Litigation, a non-governmental organisation.
The Centre filed one of the two petitions on the spectrum scam in the Supreme Court.
Bhushan, left, above, told Rediff.com, "When the information came to us how the 2G spectrum allotment was done, we got interested. We also came to know that the CBI has registered the case, but was not really investigating it. Then we saw that CBI officers who were doing a good job were transferred, suddenly. It became clear that through the CBI some cover-up was going on. So we decided to file the PIL in the Supreme Court with a plea to monitor the investigation."
"The scale of the loot and sheer brazenness of the government," Bhushan added, "motivated me to take up the case. They violated all the rules and went for the kill."
Other complainants joined the legal battle, people who had information about Swan Telecom, one of the companies alloted 2G spectrum, and Minister Raja's real estate interests.
Raja's companies and the Reliance Anil Dhirubhai Ambani Group have indirectly been beneficiaries of incorrect spectrum allotment, Bhushan claims, adding that the government must cancel the 2G spectrum allotments made to tainted companies.
When asked if he was absolving the Prime Minister's Office completely, Bhushan said, "I don't absolve the PMO totally because Manmohan Singh has been tolerating Raja till he became a big public scandal."
"Ministers in the Union Cabinet function at the pleasure of the prime minister," the lawyer said. "If he (the prime minister) is trying to say that he was really serious, then he should have removed Raja long back."
ALSO READ: Raja targeting PMO to save himself: Fali Nariman
2G scam: Why Dr Singh's credibility is at stake
The buck stops with you, Mr Prime Minister
'PM, government ignored my warnings about 2G scam'
Did Sunday night phone calls force Raja to quit?
Raja targeting PMO to save himself: Fali Nariman
Trai for no auctioning of 2G spectrum
Rs 1,70,000 crore 2G scam: CAG nails A Raja
BJP decries government's 'cover up plan' for Raja
2G scam: No action likely against Raja