An injured police source, who was allegedly beaten by miscreants on Monday night, has died at Mugdha General Hospital in the capital today.
The deceased Murad Hossain, 30, was a source of Khilgaon Police Station.
Police have detained three suspects in this connection, said Dhaka Metropolitan Police (Khilgaon Zone) Assistant Commissioner Zulfiqar Ali.
The detainees are - Mintu, Milon and Shohel. Another suspect Aziz is yet to be detained, he added.
The four suspects brought Murad at an under-construction building in Khilgaon's Shipahibag area at 11pm yesterday when he was returning home in Namapara.
Later, Murad was taken to the hospital in critical condition.
Murad helped police to arrest several drug dealers including Mintu. The suspects might killed him for this reason, the assistant commissioner said further.
Fifteen cases were filed against Mintu under the Narcotics Control Act with Khilgaon Police Station.