Central Bureau of Investigation Special Judge Bharat Parashar asked the agency whether the rule of law was followed while allocating coal block to Hindalco, a company owned by Aditya Birla Group chairman Kumar Mangalam Birla.
The CBI had booked Birla, former coal secretary P.C. Parekh and others on charges of criminal conspiracy and corruption in the allocation of coal blocks in October 2013.
The court sought the clarification while hearing a closure report filed by the CBI.
The CBI Thursday filed a closure report in the case saying that "the evidence collected during investigation did not substantiate the allegations levelled against the persons named in the FIR".
Hindalco is one of Asia's biggest producers of primary aluminium.
The court also asked the CBI to clarify whether element of criminality was involved in the case.
The investigating officer sought time from court, which posted the matter for Sep 12.