"It's not our concern what other agencies said about the former coal secretary," he said, referring to P.C. Parikh, who has defended his role in the allocation.
"We have evidence on record that it was Parakh who overturned the screening committee decision and the coal block was allotted to the Birlas.
"This is the initial stage of investigation, and a chance will be given to all accused to defend themselves. This is a Supreme Court monitored investigation and we are going by the rule book," Sinha said.
Sinha's comments came after some ministers, India Inc and others came out against the Central Bureau of Investigation, saying the CBI's action in the alleged irregularities in the coal block allocation was only creating an atmosphere of fear.
The CBI Tuesday registered a case against industrialist Kumar Mangalam Birla and former coal secretary Parekh on charges of criminal conspiracy and misuse of official position over the allocation of coal blocks.
Officials said Tuesday's FIR was the 14th in the allocation controversy.