"Primary investigation suggests rivalry among crime syndicates operating in R&H Department and Didar's refusal to give them a huge amount in toll are the main reasons behind his killing," said Deputy Commissioner of Dhaka Metropolitan Police Mazharul Hoque.

"The motive of the killing is clear to us and we are now trying to identify the masterminds behind it," he added.

Another top police official said they have already identified the three hitmen who sprayed bullets on Didar, also a first class contractor, when he was moving out of his apartment house at Mohammadpur in a microbus on Tuesday.

He however declined to disclose the names of the hitmen for the sake of 'proper investigation'.

Sources in the R&H Department also said Joy, one of the 23 listed top criminals in Dhaka, hired the three hitmen for killing Didar. All three are involved in criminal activities in Mohammadpur area.

Joy once lived at Bashiruddin Road in Dhanmondi and was known to Didar. He went into hiding after the our-party alliance came to power.

BJP is a component of the ruling coalition.

The sources alleged crime syndicates led by listed top criminals are active in the R&H Department and they force contractors to give them a certain percentage of their estimated profit as toll after obtaining a contract.

Police were still interrogating three employees of the BJP leadr's construction firm, his driver Harun and Sohrab, Akhter Hossain and Abdul Haq, who were in the microbus during the attack.

Didar's wife Dalia Nargis, who filed a case with Mohammadpur Police Station on Tuesday night, mentioned in the first information report three unidentified criminals shot her husband dead.

Police were yet to track down any of the killers.