Besides Singla, three others Sandip Goyal, Dharmendra Kumar and Vivek Kumar were also remanded by Special CBI Judge Swarana Kanta Sharma till May 8 for custodial interrogation by the agency.
"Considering the nature of the crime, custodial interrogation is essential to not only find out the source of the bribe amount but also the actual beneficiaries and conspirators other than those named in the FIR.
"I, therefore, grant police custody remand for four days," the judge said.
During the arguments, CBI told the court that Mahesh Kumar is the main accused in the case and he has been arrested in Mumbai.
It said Narain Rao Manjunath, Managing Director of GG Tronics India Pvt Ltd, was in regular touch with Mahesh Kumar who was trying to get himself appointed to a more lucrative post of in Railway Board as Member (Electrical).