Members of Rapid Action Battalion (Rab) on Saturday arrested from Gopalganj district another accused in the case over the killing of woman and her son in the city's Kakrail area.
With the arrest of Al Amin alias Jony, all the accused in the case filed with Ramna police station have been arrested.
Director (Media and legal wing) of the Rab headquarters Mofti Mahmood Khan told UNB that tipped off, a special team of Rab-4 conducted a drive in Gopalganj and arrested Jony early Saturday, he said.
Ashraf Ali, brother of victim Shamsun Nahar, filed the case with Ramna police station on Thursday night accusing Abdul Karim, 56, husband of victim Shamsun Nahar, his third wife Sharmin Akhter Mukta, 25, Mukta's brother Al Amin alias Jonny, 33.
Police earlier arrested Abdul Karim, and his third wife Sharmin Akhter Mukta soon after the killing on Wednesday night.
They are being interrogated by Ramna thana police as a Dhaka court on Friday placed them on 6-day remand in the case .
On Wednesday, Shamsun Nahar, 40, wife of Abdul Karim, and their son Shawon, 22, were found killed at their flat in a multi-storey building in the city's Kakrail area.
On information, police went to the spot and recovered their bloodstained bodies.