A high-level Narcotics Control Bureau team arrived on Saturday in Kolkata, from New Delhi, to review the progress of investigations into the major drug haul from the flat of former Central Bureau of Investigation senior officer, U N Biswas.

Customs officials had busted an international drug racket, arrested six persons including five foreigners and seized 24kgs of 'controlled' psychotropic substance, ephedrine hydrochloride, from Biswas' flat on the ground floor, on May 17.

They also recovered 842 grams of heroin from Jorasanko and Salt lake areas of Kolkata on Friday.

The Delhi team met the bureau's senior officials and discussed the interrogation of Biswas at his residence on Friday.

He was quizzed in the presence of Mizoram handicrafts emporium staff Lalthanphui, on whose reference Biswas had let out the flat to Thanga in February this year, NCB sources said.

Meanwhile, customs authorities in Shillong have discovered that N Thanga, the absconding tenant of Biswas was not a Mizo, but a Myanmarese.

The police in Shillong have questioned Thanga's wife, Gloria Remi, and 'business associate' Jolianga. They were later allowed to return home, but kept under surveillance.

Their interrogations revealed that Gloria was from a place in Mizoram bordering Myanmar, a senior official of Madandriting police station said, but her nationality was yet to be determined.