File pic: Samajwadi Party leader Mulayam Singh Yadav and his son Akhilesh

The Central Bureau of Investigation could soon close its investigation into a corruption case against Mulayam Singh Yadav for lack of evidence, say sources. The agency is expected to submit a closure report to the Supreme Court.Two months ago, a CBI officer had recommended closing the six-year-old investigation into whether the Samajwadi Party chief and his son, Akhilesh, the Chief Minister of Uttar Pradesh, had accumulated wealth beyond their known sources of income. The recommendation became public knowledge.CBI director Ranjit Sinha had at the time ordered an inquiry to determine who leaked the information, and said he would take a final call.Mulayam Singh, who props the minority government of Manmohan Singh at the Centre with the crucial support of 22 MPs, stood by the government as it weathered a particularly difficult monsoon session of Parliament, which ended earlier this month.Mr Yadav criticised key bills like the one of food acquisition in debates, but voted with the government. Political rivals allege that the Congress leveraged the case to pressure Mr Yadav into supporting it on its flagship legislation in the just-concluded session.The Yadavs, through their chartered accountant, have reportedly furnished substantial proof that for the period under scrutiny - 1993 to 2005 when Mulayam Singh Yadav was the CM of UP - their wealth grew because of loans from relatives that were later converted into gifts.Lawyer Vishwanath Chaturvedi, whose petition prompted the Supreme Court to order the CBI inquiry in 2007, has alleged that the government is leaning on the CBI to protect Mr Yadav. He filed a new petition today asking the Supreme Court to include Akhilesh Yadav's wife and Samajwadi Party MP Dimple Yadav in the investigation.The lawyer contended that the argument that Dimple was a "private citizen" when Mulayam Singh Yadav was Chief Minister does not hold as the law on corruption has provisions to include private citizens too.The top court had ruled last year that the CBI investigation could not include Dimple Yadav's assets because she was not a public official at the time. She was elected to the Lok Sabha in a by-election last year.

CBI sources told NDTV that the exemption granted to her changed the colour of the case.