The main brain behind the Common Admission Test question paper leak -- Kumar Suman Singh alias Dr Ranjit Singh alias Ranjit Don -- was planning to contest next Lok Sabha polls from Bihar, police sources told rediff.com.

Sources said Singh, after amassing huge wealth, became politically ambitious. The Central Bureau of Investigation arrested Singh along with three others in New Delhi for illegally obtaining the question paper for CAT and selling it to students.

The Patna CBI team also conducted raids at four places, including the house and clinic of Singh Sunday night.

Singh was a resident of Lodipur village under Hilsa block of Nalanda district. Sources said he was planning to stand from the Nalanda parliamentary constituency.

At present Nalanda is represented by Union Defence Minister George Fernandes, who is the president of Janata Dal-United.

"Ranjit Singh had become a millionaire within few years and had links in high society," a senior police official told rediff.com.

In 1990 he was arrested by the police in Ranchi and sent to jail in connection with a fraud case.

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Police officials involved in investigating Singh's links did not express any surprise at his arrest.

Sources said Singh's main source of income was from 'managing' the admissions of sons and daughters of 'highflying people', including politicians, bureaucrats, doctors and businessmen, in prestigious medical and engineering colleges across India.

Singh allegedly owns several houses in Patna and Mumbai. He has two brothers -- one a medical student and the other a businessman.