Terrence Black, 59, is believed to have been killed at a toilet block at the Yarra Junction football ground on May 5, 2000.

His body was found weeks later in the Little Yarra River at the back of a rural property in nearby Gladydsale on June 16.

Detectives say they have a strong suspect and believe the case is solvable, but they need help from the community.

A $100,000 reward had been offered in 2004 for information leading to a conviction but police increased it to a massive $1 million on Sunday.

Mr Black was the oldest of four siblings and his sister Pam and brothers Steve and Lindsey joined police in the appeal for information.

They say Mr Black was a peaceful man who loved Elvis Presley and fixing cars, and didn't deserve what happened to him.

"He was just an unassuming man who kept to himself," sister Pam told reporters on Sunday.

"He loved wearing good clothes and he used to wear his hair like Elvis Presley.

"We're all getting older and if we don't do something now it'll be forgotten forever."

At the time of his death, Mr Black was a pensioner and lived at the Yarra Junction caravan park.

He had been married and later divorced, and had a son and a daughter.

Homicide Squad Detective Inspector Tim Day hoped the reward would lead to answers for Mr Black's family.

"For the past 18 years Terrence's family have had to live with the thought that those responsible for his death are still out there," Detective Inspector Day said.

"We're hoping that with the announcement of this reward, there are people who reconsider their position and come forward."

Detectives wish to speak with anyone who saw Mr Black on the day he was likely killed.

"Any piece of information could prove crucial in solving this case," Detective Inspector Day said.

A reward of up to $1 million will be paid at the discretion of police for information leading to the arrest and conviction of anyone responsible for the murder.

Australian Associated Press