Police in Melbourne hope a $1 million reward for information leading to the conviction of the person responsible for the murder of Terrence Black in 2000 can bring some peace to the man's family.

Mr Black, 59, was a pensioner living at the Yarra Junction caravan park, north of Melbourne, when he was reported missing by his brother in May 2000.

His body was found in a river at the back of a rural property in Gladysdale, about 6 kilometres from the caravan park, in June 2000, about a month after he went missing.

In the course of the investigation, police received information that he may have been murdered in the toilet block at the Yarra Junction football ground.

Mr Black was a pensioner living in a caravan park when he died at the age of 59. ( Supplied: Victoria Police )

Homicide squad boss Detective Inspector Tim Day said he believed those responsible had confided in someone about the murder over the past two decades.

"The investigation has identified three strong persons of interest, one of which is a very strong suspect in this matter," he said.

"Investigators believe they are very close to solving this murder and are seeking the public's assistance to do so."

Those suspects include a woman who died in 2014, and two men, aged 58 and 68, who have previously been interviewed by police.

Mr Black's brother Steve described him as "just an ordinary guy living his life".

"He doesn't deserve to be laying in the grave while [the people responsible] are walking free," he said.

"Unfortunately he came across these mongrels that have taken it upon themselves to take his life. We won't cop that."

His sister, Pam Garamszegi said she wants to ensure her brother is never forgotten.

"I don't think there's a day in the 18 years that I haven't thought about Terry," she said.

"It would've been his 78th birthday [on Monday] and every year we go to where he's buried and every year we tell him that one day we'll find who killed him."

Police want to hear from anyone who might have seen Terrence on May 5, 2000, near the football ground, and want to speak to anyone who might know how his body was moved to Gladysdale.