Kolkata, Sep 11 : The CBI on Monday approached the Calcutta High Court's single-judge bench of Justice Amrita Sinha challenging a lower court order for joint probe in letters of Kuntal Ghosh. Recently, a special court of Prevention of Money Laundering Act (PMLA) in Kolkata ordered a joint probe by Central Bureau of Investigation (CBI and Kolkata Police on Kuntal Ghosh's letters accusing the central agencies which he forwarded to the judge of the same special court as well as to a local police station. Now CBI has challenged that order of the special court in Calcutta High Court. In the petition CBI has argued when already central agencies like CBI and Enforcement Directorate (ED) are investigating the matter of Kuntal Ghosh's letters following a clear order of the Calcutta High Court on this count, what was justification of the order of joint probe by the special court? Ghosh, an accused in the cash-for-school-job case, had charged the central agencies of pressurizing him to name Trinamool Congress' national general secretary Abhishek Banerjee in the case. CBI's petition has been admitted and the matter will come up for hearing on September 14 at the bench of Justice Sinha. CBI has already questionedthe superintendent of Presidency Central Correctional Home in Kolkata Debasish Chakraborty in connection with the 'prisoner's petition' filed by Kuntal Ghosh, an expelled youth Trinamool Congress leader. The CBI sleuths questioned Chakraborty on whether proper procedures were followed and his approval was sought by Ghosh before making this 'prisoner's petition'. The central agency sleuths also sought information about the jail employee who performed the task of delivering the letters from Ghosh to the local police station and the office of the judge of the special court. /IANS