A cigarette smoker could hold the key to an unsolved murder, police have said.
Stephen Frith, 58, was found beaten to death at a flat in Tarring Road, West Worthing, on 27 October 2017.
Detectives have been unable to identify DNA found on several Rothmans cigarette butts discarded around the property, Sussex Police said.
Det Ch Insp Emma Heater appealed for the smoker, or anyone who may know who they are, to come forward.
Mr Frith died from serious injuries "consistent with a physical assault", the force has said.
'Pain of not knowing'
His father, Ian, has described not knowing exactly what happened to his son as a "terrible pain".
Speaking on behalf of his family, Mr Frith, who lives in Lancing, said: "This not knowing what happened and having no end to the thing is really getting us down.
"My one fear is that because of my age now - I don't know how much longer I've got to go - to end up going without actually finding out what happened is really getting to me."
Three men aged 40, 38 and 20 and a 22-year-old woman, all from Worthing, have been arrested and released under investigation in connection with the death.
Crimestoppers has offered a £10,000 reward for information about the death of Mr Frith, described by family members as a "big-hearted" man.