The rare third inquest comes after years of lobbying from Johnson's family, who believe his death was a homicide committed amidst a number of gay-hate attacks in Sydney.

Johnson, a US citizen, was a PhD student who had moved to Australia to live with his partner.

Johnson's body was found near Blue Fish Point in Manly, known as a gay beat at the time of his death. His clothes were placed "in a neat bundle" at the top of the cliff.

The first inquest, held in 1989, found Johnson's death was a suicide. At a second inquest in 2012, Deputy State Coroner Carmel Forbes threw out the suicide verdict and recorded an open finding.

Counsel for Johnson's family, John Agius SC, told the Glebe Coroner's Court on Monday that a new inquest could only bring the finding of death by unlawful homicide.

Agius said there is "not a skerrick of evidence" that Johnson might have comitted suicide and that there is "no reason to suspect [Johnson], with all of his sense, could have met an accidental death."