Five years on from the death of a Flinders Island man and a coroner has still been unable to determine how he was killed.
Robert Charles Mansell died in August 2015 while fishing with his best friend Joshua Kennedy.
Mr Kennedy, who was 20 at the time, told police later Mr Mansell had been attempting to retrieve a snagged lure when he slipped into the water, and vanished.
An inquest into the 42-year-old's death revealed Mr Kennedy was a person of interest.
During the first week of the inquest in March 2018, a number of factors were raised, including the violent, and drunken arguments between the pair leading up to Mr Mansell's death.
Mr Kennedy had threatened to kill Mr Mansell during one of those arguments.
Coroner Olivia McTaggart put the process on hold, asking police to reinvestigate.
When the inquest recommenced later that year, the court heard detectives had re-interviewed Mr Kennedy, and he had responded to their questions with "no comment".
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Throughout the inquest, it was also revealed Mr Kennedy did not immediately call triple zero after his friend disappeared, claiming he could not get through.
But evidence later showed his phone was not dead, he had credit, and could have made a phone call.
Phone records also showed two calls were made from Mr Kennedy's phone shortly after Mr Mansell disappeared; one three-second call to a mutual friend of theirs and another to the phone's message bank.
Taking the stand during the last day of the inquest in March 2019, Mr Kennedy reviewed his mobile phone call record and agreed he had not made a call to triple zero.
Releasing her findings on Tuesday, Coroner Olivia McTaggart criticised the initial investigation into the tragedy.
"The investigation did not shift from the search phase to a critical consideration of the anomalies in the evidence," she wrote.
"When Tasmanian police detectives were tasked to travel to Flinders Island one month after Mr Mansell's disappearance, they were tasked in a limited capacity to address the concerns from Mr Haines (Mr Mansell's brother), rather than to instigate a full investigation based upon the possibility of homicide.
"In hindsight, a more critical approach to the suspicious features of this case was required at an early stage and may have resulted in more evidence being obtained which could have clarified the circumstances of Mr Mansell's disappearance."
Ms McTaggart found the cause of Mr Mansell's death could not be determined.
Tasmania Police Acting Deputy Commissioner Jonathan Higgins said the coroner's report would be reviewed "and where appropriate, changes to procedures will be implemented".
"Our thoughts are with Robert's family and loved ones at this difficult time," he said.
Anyone with information about Mr Mansell's death should contact police on 131 444 or report anonymously to Crime Stoppers on 1800 333 000 or crimestoppertas.com.au.
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