Senior Constable Paul Herman told the court the investigation into Fraser's death had included forensic analysis as well as public appeals for information in the form of mail drops and media coverage.
A large number of fingerprints were taken from the scene and of those 17 prints remained unidentified, he said.
Herman said the investigation had interviewed in excess of 55 people, "many of those more than once".
Coroner Shortland said the police case remained an "open file" and he did not want to say anything that could jeopardise their on-going investigation.
He did, however, conclude that Fraser died of unnatural causes in the form of blunt force trauma to the head.
At the time of the murder, Detective Senior Sergeant James Bothamley said Fraser's flatmate had been running a cannabis-growing operation inside the property and had recently harvested his plants.
The night of Fraser's death, three men reportedly arrived at the flat about 9.30pm.
The flatmate told police Fraser called out to him and as he came downstairs he saw the 51-year-old being assaulted by "a man wearing a balaclava and holding a sharp object".
"He was then ordered upstairs to show the offenders where his cannabis was located," Detective Senior Sergeant James Bothamley said at the time.
Police at the scene of Brett Gene Fraser's murder, in his Glen Eden home in 2014. Photo / Jason Oxenham
"He complied fully with their demands and handed over the cannabis, which was in three plastic containers, approximately 3L-sized each. The offenders fled.
"Mr Fraser lay wounded at the bottom of the stairs and despite first aid attempts by his flatmate and emergency services, he was unable to be revived."
Bothamley said Fraser's flatmate was also attacked and suffered head and arm injuries.
"My flatmate, he was an innocent man, they should have left him completely alone," the flatmate said in a statement provided through police.
Despite exhaustive police inquiries and a $50,000 reward, which has since expired, no one has ever been arrested in relation to Fraser's murder.
Police even said they would consider immunity from prosecution for anyone who could help them find the killer.
When the reward was offered police said while Fraser had been living in a house where drugs were being grown, "no one deserved to die on a cold warehouse floor at the hands of another".
