The CBI suspects that railway minister Pawan Kumar Bansal's nephew Vijay Singla may have swung many other postings and contracts in favour of his crony officers and contractors.
The agency also suspects the involvement of at least one more family member of the minister.
"There are 1,000 phone calls tapped by the CBI last month. The conversations suggest that there were many other postings swung by Singla in the last six months," said an investigator.
"The probe point to a racket of selling contracts and postings for a price in the railway ministry. Mahesh Kumar knew that Singla could swing the deal. He had been given assurance about it," said a souce.