DB was tasked with the case on Tuesday afternoon, Dhaka Metropolitan Police (DMP) Deputy Commissioner Muntasirul Islam said.
The DB’s Dhaka city (north) unit would conduct the investigation, he added.
Italian citizen Cesare Tavella was shot dead at Gulshan-2 on Monday evening.
His colleague in the ICCO Cooperation, Helen Vender Bik, filed a case against several unknown assailants over the murder.
Tavella was the project manager of the Netherlands-based NGO’s Profitable Opportunities for Food Security (PROOFS) programme.
Police official Islam said the law enforcing agencies were holding frequent meetings over the incident.
Plainclothesmen had been deployed around Tavella’s house, workplace, and the murder site, he added.
DMP Deputy Commissioner for Gulshan Zone Mostaq Ahmed said they were checking several angles to the murder.
Police and RAB officials said some people had been quizzed but no one had been arrested yet.
The law enforcers were also checking the footage of CCTV cameras installed in the area.
On Tuesday afternoon, physically challenged beggar Siatra Begum, a witness to the crime, was seen sitting on her wooden tool near the murder site.
Another witness, rickshaw mechanic Md Joynal, had not opened his tiny garage.
RAB and police were patrolling the street.
Sitara Begum said she had been begging on the same street for 16 to 17 years. “I even sleep here. But I have had never seen those (assailants) before. May be someone brought them from outside the area.”
The place houses several embassies.
Tavella lived in the House-11/b at Road-54 of Gulshan-2.
He said Tavella used to leave early in the morning and return late at night.
On the day of his murder, he had left the house around 9am, Hye said.
ICCO Cooperation headquarters is at Road-30 of Gulshan-1.
Its regional senior manager Raisa Chowdhury handed over a statement to journalists on Tuesday.
In the statement, the organisation expressed grief but declined to comment on the murder. It expected a thorough investigation.
Chowdhury also said the organisation was planning a press conference to reply to reporters’ queries.