Detectives have named the man they believe shot and killed Albanian scaffolder Xhem Krasniqi in Hove on Saturday night (18 May).
Sussex Police said that the suspect was Edmund Nela, 30, who lives in the Brighton area.
Detectives also wish to speak to his brother Albert, 34, who also lives locally.
Mr Krasniqi died from a single gunshot wound after he, his brother and nephew were fired at by a man they knew in Church Road, Hove, near the junction with Selborne Road.
Detective Chief Inspector Jeff Riley, from the Surrey and Sussex Major Crime Team, said: “We believe the men all knew each other and we are open-minded as to the motive.
“The initial indication is that there’s a personal dispute between some members of two families and that this has escalated dramatically, leading to Xhem’s tragic death.
“Prior to this incident police were not aware of any history between the individuals.
“We are also seeking Edmund’s brother Albert, 34, who also lives in the Brighton area. Neither of them have been seen since Saturday night.
“Both men have dual nationality – Albanian and British – and have lived in Brighton, Hove and Shoreham for some years although their home addresses are uncertain. We don’t know their occupations.
“I want to thank the public for the support and patience in this ongoing investigation. Over recent days we have made every effort to trace Edmund and Albert
“We have executed search warrants at locations around Brighton and Hove in an effort to find them.
“Neighbourhood policing officers are supporting this investigation carrying out house-to-house inquiries and visiting cafés frequented by the Albanian community, who have been very helpful.
“Over the coming days they will be visiting the area showing people pictures of Edmund and Albert in an effort to gain information about them and where they may be.
“I would urge people to talk to these officers if they have concerns.
“From the activity we have done so far we suspect that they may have left the area.
“This incident led to a man being shot dead. I want to warn the public not to approach either man, to think of their personal safety and contact police immediately, dialling 999, if they see them or know where they are.”
Anyone who sees the two men or who knows their whereabouts is asked to call Sussex Police on 999 or the independent charity Crimestoppers on 0800 555111.