Updated

A gunman in Australia who shot a man dead and held a woman hostage had been on officials' radars years ago when he stood trial for plotting a terror attack in Sydney, but eventually was acquitted, police said Tuesday.

Yacqub Khayre, 29, was one of two men cleared by a jury of plotting a suicide attack at a Sydney army base in 2010. Three people were convicted of conspiracy in that plot, which police thwarted before it could be executed.

Khayre, a Somali refugee, shot and killed a Chinese-born Australian man in the lobby of an apartment building Monday. He held a woman hostage and called police, threatening to kill her if they intervened. He also called a local TV station to say "This is for Al Qaeda," according to workers there.

Police tried to negotiate with Khayre before he walked out of the building and opened fire, injuring three officers. Khayre was later shot dead by police.

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Authorities said they were investigating the incident has an act of terror, but Victoria state police Chief Commissioner Graham Ashton said the gunman appeared to have acted alone and not as part of any ongoing plot or threat.

"There is nothing that we've found thus far that would suggest to us that this was anything that was...planned or done in concert with others," Ashton said.

However, Khayre had an extensive and violent criminal record leading up to Monday night's seige. He was sentenced in 2012 to 5 ½ years in prison on convictions including aggravated burglary after beating a woman in her home. He was initially denied parole after serving a minimum three years but was released on Dec. 8, Deputy Police Commissioner Shane Patton said.

Khayre was also required to wear a satellite-positioning ankle bracelet as a condition of his parole. Police were not advised that Khayre had removed or disabled the bracelet until the siege started, Patton said.

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Prime Minister Malcolm Turnbull said he would speak with state leaders Friday about changing state laws so that dangerous criminals are not released from prison early on parole.

"There have been too many cases of people on parole committing violent offenses of this kind," Turnbull told reporters.

During Monday's attack, Khayre spoke about Al Qaeda in phone calls to police and to Seven Network television. The Seven Network said it had received a phone call Monday afternoon from the woman in the room, telling the station she was involved in a hostage situation.

"We asked her more information, at that point a man came on the same line and said 'This is for IS, this is for Al Qaeda,'" Seven news director Simon Pristel said.

"We asked for more information and that's when he hung up," Pristel added.

Officials believe the gunman may have plotted to lure police into an ambush, However it was too early to know if the gunman set out to target police or "seized the opportunity he thought was presented to him," Ashton said.

He added that there was nothing to link the violence with a van and knife attacks in London in which three assailants killed seven people.

Ashton said there was nothing to link the violence with a van and knife attacks in London in which three assailants killed seven people.

Police did not regard the Islamic State group's claim of responsibility for the Melbourne violence as evidence that it was planned.