It's a question that has so far gone unanswered and one former coroner Don Jones said is likely to remain so for eternity, despite many police investigations and a lengthy coronial inquest.

Next Sunday is the 20-year anniversary since the Italian backpacker mysteriously met her fate while sunbaking on Beaumaris Beach.

There are many people police labelled as potential suspects, yet no conviction has been made.

"I don't believe that some of the people police pursued in particular did commit the crime, but I do think there are people out there who do know who committed the crime," Mr Jones, a retired Burnie magistrate, said.

"I think that possibly there was a person who learned of the crime later and may have assisted in some way.

"When one considers the evidence of the body, the person would be covered with blood — a lot of blood it's something that would have been noticed by somebody else.

"There was a weapon that was never located despite attempts to get a similar knife to what was used that was never successful."

The inquest covered nine years of information, 250 official statements and 1100 police reports.

The inquest began in March 2003 and at the start of the investigation, Mr Jones took an unprecedented step in establishing a hotline for people to call to pass on information, before a 13-month delay.

The inquest resumed in St Helens during April 2004 and Mr Jones handed down his findings on March 23, 2005.

Mr Jones rejected such conspiracy theories that the killer came ashore via a boat, stabbed Miss Cafasso and returned to sea.

He labelled that and others as "rubbish" and "pie in the sky".

A serial killer was ruled out and the motive was unlikely to have been rape or sexually motivated.

It has been well documented that police made several errors in the early stage of the investigation including the state forensic pathologist's non-attendance, delay in a specialist examiner reviewing evidence, failure to close the beach, scene contamination and no video being recorded — among other oversights.

During the inquest Mr Jones uncovered photographs taken by one of the original attending officers that were not tendered as evidence.

They revealed conflicting facts.

"I believe that even if they were to ever to locate the person who did the crime, the evidence was so tainted at the time, it's most unlikely now they could ever get a conviction," Mr Jones said.

"There was a statement by the police that the body had never been tampered with by way of having clothes put over it, or in particular a blue tarpaulin.

"This was denied by police that it ever happened, it was only subsequently during the inquest that I became aware of new photographs that had never been produced in the past and they showed the body clad in a blue tarpaulin.

"They also showed other photographs where there was a number of footprints around where the body was in fact located and there was also around the scene itself, which they called the death scene as well.

"I think it could have been better investigated."

He said the mysterious murder was devastating for the Beaumaris community and one in conjunction with German backpacker Nancy Grunwaldt's disappearance, gave Tasmania a bad reputation internationally.