Sources said the agency has recovered some documents during searches at his official residence in Mumbai while some were found from a different location where they were hidden by a Railway Protection Force inspector.
They said agency is trying to find out whether a case of disproportionate assets can also be slapped against Kumar who is already facing allegations of corruption.
The officer is in judicial custody along with Bansal's nephew, Vijay Singla and other middlemen who were also nabbed in connection with the bribery scandal, they said.
The case relates to reported aspirations of Kumar for his elevation as Member (Electrical) in the Railway Board for which he allegedly contacted Goyal, a close associate of Bansal's nephew Vijay Singla. Goyal had allegedly demanded Rs 10 crore for it.
The agency alleged a part payment of Rs 90 lakh was made to Singla, after which it carried out searches at their premises and recovered the alleged bribe amount. CBI has so far arrested eight persons in the case.
