Sylhet Metropolitan Police’s Additional Deputy Commissioner Rahmat Ullah told bdnews24.com that the police headquarters gave the order on Monday.
“It asked police to hand over the investigation to the CID,” he said.
Secular blogger Das, also an organiser of Ganajagaran Mancha, was hacked to death on May 12 at Sylhet’s Subidbazar.
His relatives claimed he had received threats for his writings.
Das’s brother filed a case with Airport Police Station the next day. Police failed to identify or arrest anyone over the killing.
He was the third blogger to be killed in three months.
A purported Twitter profile of extremist group ‘Ansar Bangla 8’ said the al-Qaeda in Indian Sub-continent (AQIS) claimed responsibility for the killing.
Al-Qaeda’s Indian offshoot had previously claimed credit for the killing of those who it branded ‘blasphemers’.
Investigators say they are considering the terrorist organisation’s involvement in the killings.