A 68-year-old prison inmate died at Dhaka Medical College Hospital (DMCH) after being taken there from Keraniganj Central Jail in critical condition.
The deceased was identified as Md Majid Ali.
He was brought to the hospital's emergency department late Wednesday by several prison guards, including Aminul Islam, following instructions from the prison authorities.
After examination, the on-duty physician declared him dead at 1:05am on Thursday.
Inspector Md Habibur Rahman, in charge of the DMCH Police Camp, confirmed the death.
He said the body had been kept at the hospital morgue for an autopsy.
The case in which Majid Ali was detained could not be immediately confirmed.