Nair's statement was both recorded on video and noted down by police on June 23 when she was questioned by Special Investigation Team (SIT) at Chengannoor, Vijayakumar told reporters here.
"The Home Ministry is hiding the statement and police has not included it in their case diary. It is based on a secret agreement between the Home Minister and Chief Minister. Police and Home Ministry should reveal the truth immediately," he said.
"I strongly demand that it should be brought under the anti-corruption law. The case should be probed by a judicial panel under the guidance of the High Court," he said.
The solar scam pertains to financial cheating of a large number of people by Nair and Biju Radhakrishnan. It took a political turn after the arrest of a close personal aide of Chief Minister Ooman Chandy for his alleged links with the fraudsters.
Two other personal staff members of Chandy were removed and state Public Relations Director A Firoz was also arrested in a related case.