The Central Bureau of Investigation Saturday began interrogating underworld don Abu Salem [Images], extradited from Portugal and arrested for his alleged complicity in 1993 Mumbai serial bomb blasts, with the central intelligence agencies likely to join CBI in the probe soon.

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The CBI started interrogating Salem at an undisclosed place in south Mumbai in the afternoon where a team of interrogators started with the routine procedure of recording the history of the gangster, CBI sources said.

"We will record everything, from his past, before taking to crime, to his present status, so that our other teams start analysing it and prepare an interrogation strategy for the coming days," they said.

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A team of senior CBI officials was giving final touches to a questionaire prepared to quiz Salem, which he will be asked to answer in writing. In case the gangster expresses unwillingness to reply in writing, the same will be recorded indepth by the interrogators, they added.

"We are not in a hurry to interrogate him. The details of his involvement and the evidences to substantiate are already with us. What we plan to do is find out more intricate details from Salem, which may help us explore corroborative evidence in the case," the sources said.

A team of doctors Friday examined Salem as part of the routine medical examination. Salem, who was brought to Mumbai from Portugal Friday morning, has been charged under the Terrorist and Disruptive Activities Act and will be in CBI custody till November 23.

The CBI has formed a number of teams headed by inspectors that will verify the information coming out of Salem's interrogation. These teams will give feedback to the interrogators, the sources said.

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Meanwhile, sources said the central intelligence agencies' units based in Mumbai will also be monitoring the probe on a day-to-day basis and may join the probe as and when required.

"Salem is a wealth of information. He has closely been associated with the Dawood Ibrahim [Images] gang, and knows the strengths and weaknesses of Dawood and his rival gangs better. The tit-bits he might give us during the course of interrogation can help us tying some loose ends in the intelligence of these gangs," the sources added.

Meanwhile, Salem, produced in TADA court Friday, had been reportedly in Mumbai Crime Branch custody due to security reasons, the sources said but refused to confirm. Mumbai police officials refused to comment on the issue.