New Delhi: Samajwadi Party MP Rewati Raman Singh on Monday appeared before Delhi Police for questioning in connection with the 2008 cash-for-vote scam, the fourth person to be quizzed in the past 10 days after the Supreme Court came down heavily on investigators for carrying out a shoddy probe.

Rewati Raman, the 68-year-old Allahabad MP, reached the Crime Branch office in Chanakyapuri.

The questioning of Rewati Raman comes three days after his former party colleague Amar Singh was questioned by the investigators. Two persons Sanjeev Saxena, former aide of Amar Singh, and Suhail Hindustani, an alleged go-between Amar Singh and BJP sought to be bribed, were arrested after quizzing.

The aim of questioning is to ask Rewati Raman about the telephone call he received from Hindustani on the midnight of July 21 and 22 to strike a deal to buy BJP MPs, a senior police official said.

Police had already given a virtual clean chit to Rewati Raman and others saying it was Hindustani only who tried to approach them for striking a deal for MPs to vote in favour of the UPA government.

Investigators believe that Hindustani is the "master orchestrator" of the scam and he tried to entrap leaders of Samajwadi Party and it was this purpose that he telephoned Rewati Raman.

Police claimed that none of the Congress leaders or SP leaders mentioned by Hindustani had made any effort to contact him to strike a deal.

Investigators are also preparing to question BJP MP Ashok Argal, who was allegedly given the bribe money, and BJP leader L K Advani's former aide Sudheendra Kulkarni this week before police submit its status report to Supreme Court this Friday.

The probe in the three-year-old scam gathered momentum last week after the Supreme Court came down heavily on Delhi Police for its "callous" investigations in the case.

Reacting to the summons issued to Rewati Raman and questioning of Amar Singh, SP chief Mulayam Singh Yadav on Sunday said it was "injustice" and a "conspiracy to trouble" both the Parliamentarians.

Yadav claimed that former SP leader Amar Singh was not involved in bribing of BJP MPs. "We only helped by voting in their (Congress') favour. Did we join the government? Did Amar Singh or Rewati Singh become ministers? Had money changed hands, I would have known about it," he claimed.