The CID on Monday began its inquiry into the death of Faiz Usmani, the brother of an alleged Indian Mujahideen member, who died in a hospital on Sunday following questioning by the Crime Branch sleuths in connection with July 13 serial bomb blasts in Mumbai.
Faiz was the brother of Afzal Usmani, currently lodged in jail for his alleged role in 2008 Gujarat blasts.
The CID inquiry was ordered by Maharashtra director general of police after Usmani's family alleged that he was tortured in police custody.
The statements of Usmani's family members, as well that of Chembur Crime Branch unit in-charge Sripad Kale, were yet to be recorded, a CID official said.
Meanwhile, Mumbai's deputy police commissioner (Crime) Nisar Tamboli described Usmani's death as "unfortunate" and said "it is natural for any person to make allegations when a family-member dies".
"We had brought him from his Govandi residence for questioning on Saturday but Usmani did not appear to be tense or anxious. About 20 to 25 minutes after he was brought to the Chembur Crime Branch unit, he felt unwell after which he was immediately rushed to Shatabadi hospital," Tamboli said.
"Doctors at Shatabadi hospital advised us to take him to Sion hospital and there was no delay on the part of police in taking him to the hospital and we provided all possible medical assistance to Usmani," Tamboli added.
The controversy over Faiz's death has caused a setback to investigations into the blasts, a police officer said on the condition of anonymity.
19 people were killed and over 130 were injured as blasts ripped through crowded areas of Zaveri Bazaar, Opera House and Dadar West on July 13. So far, no one has been arrested.