Investigations into the human smuggling case picked up pace on Thursday with police questioning two lawmakers in connection with the high-profile case and arresting a key middleman in the emigration racket.

Mohammed Tahir Khan of the Bahujan Samaj Party and Bharatiya Janata Party's Ramswaroop Koli, whose names were taken by an alleged conduit arrested in the case, were questioned at length by the Crime Branch officials after they presented themselves in response to their notice.

Investigators verified their travel documents to find out details about their foreign trips and asked whether they knew Sunder Lal Yadav, who claimed to have introduced couple of travel agents to them, sources said.

Police sources said the MPs denied any role in the human smuggling racket and were evasive when posed questions about the claims made by Yadav, a betel shop owner, in a court in New Delhi and during his interrogation.

Investigators sought to know whether the MPs knew Yadav or Rashid, a Hyderabad-based travel agent, who was arrested by the Andhra Pradesh police last week in connection with a fake passport case there.

Yadav had told police and a court in New Delhi last month that he had introduced Rashid and some other travel agents to the MPs, adding a new twist to the trafficking case which came to light after the arrest of BJP MP Babubhai Katara.