A Melbourne man revealed that the Christchurch accuser had sent him death threats more than two years before the mosque shooting.
The man had denounced the threat to the Australian police in 2016 – and was said only to block the alleged sniper on Facebook.
The man said the defendant sent him a death threat after criticizing the United Patriots' Front (UPF).
He kept screenshots of the threats made in August of that year, ABC reported.
The contact was made via Facebook messenger and the gunman of the accused mosque told the man: "I hope one day you will find the rope."
The Australian-born gunman defended the UPF, which is an anti-immigration group, as "the main ethnic-nationalist group within Australia."
"When you speak against the UPF, you speak against my right to a home for my people and my culture," he wrote.
"That marks you."
The accused accused the man of "carefully choosing his words" and "thinking of who you insult."
"I hope one day you will see the light, and if you are a Marxist, I hope that one day you will find the rope."
The threat recipient reported the incident to the police in September 2016.
He provided a copy of the conversation and told police he believed the defendant was dangerous, ABC said.
The man said that the police did not make a formal statement – and instead told him to block the creator of social media threats.
After the attack on the Christchurch mosque, which claims 50 lives, the man was shocked to discover the identity of the alleged culprit.
"I feel guilty and have been beaten," he told ABC.
"But at the time I thought I was the only one in danger."
Victoria police said they were "unable to locate a complaint made by the victim in 2016."
"Although we do not comment on this particular case because of the lawsuit in New Zealand, we assure Victorians that we have strong agreements to monitor and track people who pose a threat to the community."
The shooter accused of Christchurch appeared at the Christchurch High Court last Friday.
He faces 50 counts of murder and 39 counts of attempted murder.
He made no appeal for his alleged attack on the two mosques, one on Deans Avenue and one on Linwood Avenue.
Thirteen people are still in hospital weeks after the shootout.