Australia's prime minister Tony Abbott said the gunman who took hostages inside a cafe in Sydney, Australia was a "deeply disturbed individual" who was known to police, but not on any terror watch list

Abbott said at a press conference Tuesday that he does not believe Man Haron Monis was on any watch list, though he had been "well known to the Australian Federal Police."

The 50-year-old hostage taker, who was reportedly armed with a pump-action shotgun and a machete, stormed the Lindt Chocalat Cafe at the height of rush hour Monday morning, triggering a 16-hour standoff seen by much of the world on television.

Throughout the day, several hostages were seen with their arms in the air and hands pressed against the window of the cafe, with two people holding up a black flag with the Shahada, or Islamic declaration of faith, written on it.

The siege ended amid a series of explosions, believed to be gunshots and flash grenades, as police stormed the cafe. When it was over, Monis, a 34-year-old man and 38-year-old woman were dead. Four people were injured in the raid, including a female hostage who was shot in the leg, an official told The Associated Press, as well as one policeman, who suffered a gunshot wound in the face, who was reported to be in good condition, authorities said.

No motive had emerged for the attack by early Tuesday afternoon.

But the Prime Minister said Monis had "a long history of violent crime, infatuation with extremism and mental instability."

Monis, who reportedly emigrated to Australia in 1996, was known in Australia for his public campaign of writing letters to the families of soldiers killed in Afghanistan, calling them “murderers,” and urging the recipients to lobby the government to withdraw from Afghanistan. He was charged in 2009 with using the postal service to harass, and was convicted and sentenced last year to 300 hours of community service for sending what a judge called "grossly offensive" letters.

At the time, Monis said his letters were "flowers of advice," adding: "Always, I stand behind my beliefs."

Monis later was charged with being an accessory to the murder of his ex-wife. Earlier this year, he was charged with the sexual assault of a woman in 2002. He has been out on bail on the charges.
Talat Khalik, the godfather of Monis' ex-wife, Noleen Hayson Pal, told NBC News Tuesday that "he should have been hanged a long time ago."

“But you’re innocent until proven guilty," he added.

Abbott said Monis "had a long history of violent crime, infatuation with extremism and mental instability."

"This is a one-off random individual. It's not a concerted terrorism event or act," his former lawyer, Manny Conditsis, told Australian Broadcasting Corp. "It's a damaged-goods individual who's done something outrageous. His ideology is just so strong and so powerful that it clouds his vision for common sense and objectiveness."

Monis ran a website which was taken down shortly after he was named as the gunman in the hostage situation, Sky News reported. In a letter posted to the website, which he signed Sheikh Haron, he accused Australia, Britain and the U.S. of "oppression and terrorism" and posted images of dead children.

Monis also reportedly called for non-violent activism, writing that "Islam is the religion of peace and a Muslim should be a peace activist."

The Sydney crisis comes less than two months after a "lone wolf" attack shook Ottawa, Canada, when Michael Zehaf-Bibeau, in what authorities called a terror attack, stormed the county’s national war memorial and shot a soldier to death, then entered the Canadian Parliament before being killed by police.

In the aftermath of the Ottawa attack, lawmakers on Capitol Hill said Internet propaganda spread by jihadist groups could radicalize individuals. In particular, such concern is in large part in response to the Islamic State’s aggressive, online propaganda campaign.

"You have to ferret it out,” California Democratic Sen. Dianne Feinstein, chairwoman of the Senate Intelligence Committee, told CNN's "State of the Union” in October. “You have to be able to watch it, and you have to be able to disrupt them."

The Associated Press contributed to this report.