Members of Rapid Action Battalion (Rab) detained five people including the son of the victim, who was shot dead in Rab firing in Sonargaon upazila early Saturday.
Nazrul Islam, son of 65-year-old Abdul Kashem, who died when RAB resorted to firing, was among the detainees.
Meanwhile, Nasir Uddin, warrant officer of Rab-11, filed a case against 21 identified and 79 unidentified people in connection with the incident on Sunday, said Mahbub Alam, officer-in-charge of Sonargaon Police Station.
The detainees were handed over to Sonargaon Police Station.
However, the families of Kashem did not lodge any complaint in connection with his death yet.
Earlier on Friday, a team of Rab in plainclothes conducted a drive in Borogaon area of Sonargaon upazila to detain a suspect accused of a murder case around 1:30 am (Saturday).
At one stage, local people obstructed Rab and tried to snatch away the accused, said Rab. The locals however said Rab were in plainclothes and refused to identify themselves, hence they tried to prevent taking away their neighbour. Some of them even called 999 fearing they were miscreants.
By the time RAB did identify themselves, the situation had gotten out of control. Abul Kashem was killed by a single bullet to the chest, and another person was shot in the legs.
Rab then detained 20 people for interrogation. After some time, 15 of them were released.