The crime branch investigated the case on Singh who has been indicted in the scam for allegedly sending money as bribe to win over three BJP lawmakers during the 2008 trust vote in the Parliament. The Home Ministry earlier had issued the go-ahead to question Amar Singh.
Earlier, the Delhi police had arrested Singh's former aide Suhail Hindustani over the scam. Hindustani shocked many when he mentioned Prime Minister Manmohan Singh and Congress president, Sonia Gandhi's names in the whole cash-for-votes scandal.
During the grilling time on Wednesday, Hindustani had claimed, "I received calls from Amar Singh and Ahmed Patel (Political Secretary to Congress President Sonia Gandhi). Those close to Prime Minister (Manmohan Singh) called me and even from 10-Janpath (Gandhi's residence)."