Mr Johnson's sister Terry Johnson said Scott White, who pleaded guilty to the murder in January this year, had taken away decades from her brother's life.
"The hateful person who killed Scott has been walking free on this earth for the past 33 years. Thirty-three years that he took away from my baby brother. I believe [White] deserves life in prison."
With White looking on from the NSW Supreme Court dock, sister Rebecca Johnson talked about how society in the 1980s had also let down teenagers who thought violence against gay men was acceptable.
"Parents, brothers and sisters, teachers and classmates, authority, culture, somehow Mr White's world reinforced that violence and even killing was OK and maybe that gay men weren't human. That is a profound tragedy," she said on Monday.
Ms Johnson questioned why her brother, an American mathematician, was placed in the crosshairs of deadly violence and murder simply for who he chose to love.
Brother Steve Johnson described the death as too awful to be true, saying his mother had reacted with a wailing cry at the news.
"The wailing is a reliving, it's a howl of death and despair and loss and grief that signifies that a piece of us has departed. It never goes away."
Scott Johnson's partner Michael Noone also gave a statement describing the sheer horror of receiving a call from the police about the death of a loved one.
These victim statements were heard after White's former partner Helen White took the stand and described a conversation with him in December 1998 about his "poofter bashing" of the 1980s.
"He said the only good poofter is a dead poofter, to which I said, 'So you threw him off the cliff'. And he said, 'It's not my fault the dumb c*** ran off the cliff'," she said.
Ms White denied suggestions by White's barrister Belinda Rigg SC that she had only gone to police because of a $1 million reward offered in 2018 for information about Mr Johnson's death, and rejected claims she had made up the conversations with her then husband.
Ms Rigg argued that White should receive a lesser sentence because he had only turned 18 at the time, saying that sentences for murder were significantly lower in the late 1980s and early 1990s.
White's intellectual impairments meant he had suffered stress, anxiety and panic attacks while in custody. During the 1980s, White was a gay man who had lived with his homophobic brother and alcoholic parents, Ms Rigg said.
The prosecution pointed to the seriousness of the offence, saying it was targeted towards the victim's sexuality.
"This was a grave and serious murder which entailed a high degree of criminality," crown prosecutor Brett Hatfield said.
Speaking after Monday's hearing, Steve Johnson said that while giving their statements in court was emotional for the family, it was a chance to look White right in the eyes.
"I got to tell [White] what my brother was like. I got to tell him how it felt to hear that he was dead ... I have to think it sunk in. He watched and listened."
White's defence team unsuccessfully tried to reverse the guilty plea the day it was made. An appeal of White's conviction was filed last month.
While the initial police inquest in 1989 found Mr Johnson's death was a suicide, the case was reopened in 2012. Another inquest returned an open finding in June 2012, but a third in 2017 found Mr Johnson fell from the clifftops as a result of violence by an unidentified attacker who perceived him to be gay.
Justice Helen Wilson will hand down her sentence on Tuesday.
