Gun 'testing' in hunt for accused cop killer fugitive

It's emerged that a single gunshot was heard after two police officers were killed at Porepunkah. (Simon Dallinger/AAP PHOTOS)

A reported single gunshot has sparked a fresh line of inquiry in the long-running manhunt for alleged police killer Desmond Freeman.

Police conducted "firearms testing" near Barrett Lane and Rayner Track in Porepunkah, about 300km northeast of Melbourne in Victoria's northeast, on Wednesday as part of their search.

The testing was triggered by reports of a gunshot in the vicinity about 11.45 am on August 26.

Freeman had allegedly opened fire on police moments earlier, killing Detective Senior Constable Neal Thompson and Senior Constable Vadim de Waart-Hottart and wounding a third officer.

An extensive search over several weeks has failed to find any trace of suspect Desmond Freeman. (Simon Dallinger/AAP PHOTOS)

They were among 10 officers serving a warrant at Freeman's Porepunkah home when allegedly confronted about 10.30am.

"The area has since been searched by police, however no trace of Freeman was located," Victoria Police said in a statement on Sunday.

"Investigators are hopeful that the firearms testing may assist police with the ongoing search."

Police want to speak to anyone who may have heard the gunshot, including any members of the public who may have been in the area at the time and believe they could be the person responsible.

There have been no confirmed sightings of Freeman since he fled into dense bushland despite detectives investigating more than 1700 tip-offs.

Hundreds of officers and specialist resources, including interstate and international crews, have scoured the area and surrounds.

The search was scaled back to more than 200 police in September and Mount Buffalo National Park reopened to the public in late October.

The two men were among 10 officers serving a warrant at Freeman's home, when they were gunned down. (Con Chronis/AAP PHOTOS)

Chief Commissioner Mike Bush has previously said police were working off several possible scenarios.

"Is he still alive? We don't know. Is he alive and still in the area? We have no real information to suggest that," Mr Bush told reporters on October 13. 

"Or has he been unable to leave the area and is being looked after by others? We don't know.

"All of those are assumptions, possibilities, and we plan a resource for those three."

Victoria Police has offered a $1 million reward and the possibility of indemnity for information leading to Freeman's capture, the largest reward in the state's history for facilitating an arrest.

People in the area have been advised to remain vigilant and not approach the fugitive, who is considered armed and dangerous.