Two cases were filed on Wednesday night over the killing of a businessman Abdul Rashid at Uttara's Dakshinkhan area in the capital.
Harun-ur-Rashid, elder brother of the victim, filed the cases.
A number of 31 people were accused in the cases while names of 13 were mentioned.
Police have already arrested eight persons for alleged involvement in the killing, confirmed Hafizur Rahman Real, additional deputy commissioner of Police in Uttara division.
He said, "Police arrested eight persons who had been sent to jail after being produced before the court."
The arrestees are Aminul Islam Hannan, prime accused of the cases, Akramul Islam, Shafiqul Islam Imran, Al-Amin Pradhan, Jahirul Islam Ripon, Khorshed Alam, Mosharaf Hossen and Nurun Nobi.
Abdul Rashid was shot and killed by an alleged extortionist at Dakshinkhan area of Uttara in the capital on Wednesday.