A digitally "aged" image depicting a man in his 60s has been released by police investigating the assassination of a Turkish diplomat and his bodyguard in Sydney nearly 40 years ago.

Sarik Ariyak, 50, was gunned down alongside his bodyguard Engin Sever, 28, in Dover Heights in December 1980, in a politically motivated attack claimed by the Justice Commandos of the Armenian Genocide.

Two unknown men approached Mr Ariyak and Mr Sever as they left a Portland St residence and fired multiple shots at close range before fleeing on a motorbike.

Police are re-investigating the murders and have released the original computer-generated images of the unknown men, based on witness descriptions, along with a computer-aged image of one of the males.

Both men are expected to now be in their mid-to-late 60s.

Earlier this month a $1 million reward was also announced for information leading to a conviction, as Mr Ariyak's daughter Cagla returned to Sydney to attend a memorial service for her father.

READ MORE US House recognises Armenian 'genocide', despite Turkish rebuke

Ms Ariyak was just a young girl when her father was killed moments after kissing her and her mother goodbye as he left the house.

"It was, of course, quite a shock - it happened in front of us," she told reporters.

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She was quickly taken to a neighbour's house but watched the aftermath from a window.

"I felt horrible," she recalled.

Assistant Commissioner Mark Walton urged anyone who may recognise the men to come forward.

AAP

"While we are only in the initial stages of the re-investigation, we suspect there are people who know exactly what happened that day but have not yet been willing to speak with authorities," he said in a statement on Sunday.

with AAP...