After the arrested duo in cash-for-vote scam - Sanjeev Saxena and Sohail Hindustani - named Rajya Sabha MP Amar Singh, he was called for questioning by the Delhi police crime branch on Friday.
Singh reached the crime branch's office around 10:45 am and was questioned for more than three hours.
During the questioning, police asked him over a dozen questions related to the money trail and about his personal connection with Saxena and Hindustani.
Highly placed sources in crime branch said Singh denied his link with Saxena and said he might be an employee in one of his many companies.
"Singh cooperated with the investigating agency and if required he will be called for questioning again. Now we are concentrating on status report that we need to submit in the Supreme Court next week," said a senior police officer requesting anonymity.
Singh was questioned in front of Saxena and Hindustani.
To carry the investigation forward, police have now served a notice to Lok Sabha MP Rewati Raman Singh and is likely to question him on Monday.
"Now we need to examine Rewati Raman Singh and BJP MP Ashok Argal and both will be questioned .... We have served a notice to Raman Singh and he has been asked to join the investigation on Monday," the officer added.
Meanwhile Hindustani and Saxena were sent to Tihar Jail by a Delhi court after the city police probing the case told it that they were no longer required for interrogation. Both are remanded to judicial custody till August 5.