Police investigating the death of Croydon man Michael Polding are offering £5,000 to trace his friend.
Detective Chief Inspector Nick May appeared on Crimewatch, four months after Mr Polding's death.
He is offering the reward for the arrest of Ricardo Pisano, who is also known as Brandon Victor Pillay and uses the nicknames "Ree" or "Ricky".
Mr Pisano who has a south African accent, is believed to be in his thirties and has links to Croydon, Crouch End, Southampton and New Zealand.
Mr Polding, who was 62 and openly gay, moved from Croydon to St George's Road in the Kemp Town area of Brighton nine months ago.
His body was discovered at his flat on July 16, but it is thought he may have been dead since May.
DCI May said: "It is now four months since Michael died and his family are anxious for answers about what happened to him.
"We are still unclear as to when exactly Michael died and our enquiries have shown he was friends with Mr Pisano.
"We think he may have information about Michael's last movements, however we have been unable to find him so far.
"We want to help provide the answers for Michael's family and hope the reward will prompt someone to reveal Mr Pisano's whereabouts.
"All we need to know is where he is so we can talk to him about what he knows."
Anyone who recognises Mr Pisano and knows where he may be should contact Sussex Police on 101 quoting Operation Journal, or Crimestoppers anonymously on 0800 555 111.