Detective's memorial to Andy Marshall

A detective who investigated the death of Andy Marshall, who was pushed from the top floor of the Ocean Beach Hotel in 2011, has raised thousands of dollars to pay for a memorial in his honour.

Mr Marshall's parents Alan and Wendy will travel from New Zealand to unveil the memorial plaque outside the hotel on Friday, the fourth anniversary of their son's death.

Sgt Matt Donkin, who hoped to raise $2500, collected more than $4100, thanks to the public's generosity and the extra money was used to help the Marshalls attend the ceremony.

Alan Marshall said yesterday it would be difficult to return to the site on the anniversary but hoped it would send a powerful message about the devastating consequences of one bad decision.

Former Rock Machine bikie prospect Stefan Schmidt was initially found guilty of murdering Mr Marshall, 29, after pushing him out of an upper window at the pub in May 2011, causing him to plunge 7m to his death. But after his conviction was quashed on appeal, he returned to court in May last year and was convicted of manslaughter.

Supreme Court Justice John McKechnie described it as an appalling crime and one of the worst cases of unlawful killing imaginable.

Seconds after seeing the musician talking to his female acquaintances, an angry Schmidt pushed him to his death. He was sentenced to nine years jail, and with parole and time served he could be released in mid-2018.

Mr Marshall said his family lived with their son's death every day but were trying to find the strength to help others.

They said the plaque would be more than just a place to honour their son.

"We want people to stop and think about the power of one decision, one senseless act of violence and the downstream consequences . . . the tragedy and irreversible heartache that impacts on so many people," they said.

There will be a public unveiling of the plaque at 10.30am.