Salt Lake: The CBI has arrested a Calcutta High Court lawyer for allegedly demanding money from a trader after threatening to implicate him in a narcotics case.

Danish Haque was rounded up when he was allegedly collecting the first instalment of bribe money from Pratap Aditya, a city-based businessman, late on Monday at his chamber in Park Circus.

Based on what Danish told investigating officers of the central agency, the CBI later arrested Amarendra Kumar Singh, an officer of the Narcotics Control Bureau (NCB), on the charge of colluding with him.

"There was a specific complaint and we laid a trap. The accused have been remanded in our custody," said an officer of the CBI.

CBI sources said Pratap had lodged a complaint with the agency alleging that Danish had threatened to frame him in a case related to illegal possession of party drugs if he did not pay up Rs 2 lakh.

"Pratap had even submitted some of the recordings of his telephonic conversation with the two along with his complaint," an officer said.

Based on the allegation, the agency drew up a case and a probe was initiated.

On Monday, a team of officers from the anti-corruption wing of the CBI followed Pratap while he was on his way to meet Danish with Rs 50,000 late at night.

As soon as Pratap handed over the money to Danish, the officers in plainclothes arrested the lawyer.

After quizzing Haque, the team headed for Rajarhat and picked up Singh.

"It appears Singh would threaten targets and Danish would offer to settle the case against a hefty payment," the officer said.

NCB officials said they had started an internal probe to find out whether Singh was actually involved in the case or was framed.

CBI officers said they would try to find out whether any case related to illegal possession of party-drugs had been pending against Pratap.