A screengrab taken from Monis' website, before it was taken down. Photo / AAP
On Monday morning, he entered the Lindt cafe in central Sydney armed with a shotgun and took 17 people hostage.
The 16-and-a-half hour siege claimed the lives of mother of three Katrina Dawson, shop manager Tori Johnson and Monis.
Monis' website, which included a graphic photo of dead children who appeared to be victims of an air strike in the Middle East, has been taken down.
It gave a glimpse into the motivation of the man described by his former lawyer, Manny Conditsis, as a "damaged goods individual".
It also suggested he had recently turned towards a radical branch of Sunni Islam, having rejected his adherence to Shia Islam.
The Sunni-based Islamic State and other jihadist groups consider Shi'ites to be heretics.
Monis, who called himself Sheikh Haron but was labelled the "fake sheik" by the media and his own community, was born in Iran and came to Australia as a refugee almost 20 years ago.
Serious concerns were raised about him from within the Muslim community as far back as 2008, when Sydney-based Shi'ite cleric Kamal Mousselmani urged federal agents to launch an investigation into Monis.
Sheik Mousselmani said none of his fellow spiritual leaders knew who Monis was.
"The federal police should investigate who he is," Sheik Mousselmani told News Corp Australia at the time.
The Iranian government also claims it had warned Australian authorities about Monis's mental state.
"The psychological conditions of the person who took refuge in Australia two decades ago had been discussed several times with the Australian officials," a foreign ministry spokeswoman told Iran's Fars news agency.
"The situation of the hostage taker had been completely clear to the Australian-related officials."
Monis came to the attention of police when he sent hate-filled letters to the families of dead Australian soldiers seven years ago.
On bail after being charged with being an accessary to the murder of his ex-wife, he also faced dozens of indecent and sexual assault allegations before his death yesterday.
Monis previously on watchlist
Man Haron Monis was previously on Australia's national security watchlist, but had been taken off in recent years, according to Australian media reports.
Questions were being asked yesterday how he was able to carry out such an attack under the noses of authorities, with Prime Minister Tony Abbott telling media he had not been on the country's security watchlist.
However, this morning the Daily Telegraph reported that Monis had previously been on the radar of Australia's intelligence agencies for several years for his extremist behaviour.
A senior government source told the newspaper Monis had been "of interest" to the authorities in the late 2000s. But he had recently been taken off a security watchlist, after it was deemed he no longer met the threshold for monitoring, the paper said.
"He had been the subject of security interest, yes," a senior intelligence source was quoted as saying.
"But he had dropped off."
Monis was on the watchlist prior to 2010 after his activities came to the attention of intelligence and counter-terrorism agencies in Australia, the paper claimed.
A number of intelligence reviews are already underway into how Monis - who was described as being infatuated with extremism - was able to slip past authorities.
- AAP, additional reporting NZME. News Service
