Just a day before he held hostages at gunpoint in Sydney, Man Haron Monis claimed to be a peace activist, and among Muslims who are fighting "against the oppression and terrorism of USA and its allies".

In a post dated December 14 on his now defunct website, 50-year-old Monis wrote: "Islam is the religion of peace, that's why Muslims fight against the oppression and terrorism of USA and its allies including UK and Australia.

"If we stay silent towards the criminals we cannot have a peaceful society. The more you fight with crime, the more peaceful you are. Islam wants peace on the Earth, that's why Muslims want to stop terrorism of America and its allies. When you speak out against crime you have taken one step towards peace."

Monis, who referred to himself as "Sheikh Haron", had also posted an open letter to all Muslims in October, claiming that they should work toward peace.

"Islam is against oppression and any unfair violence. Islam is against terrorism. As I have repeatedly said earlier: this pen is my gun and these words are my bullets, I fight by these weapons against oppression to promote peace," he wrote.

He also penned a letter to Australian Prime Minister Tony Abbott, insisting that "It is proven that Australia and Australians will be attacked".

Monis was well-known to police, having been involved in a hate mail campaign against the families of Australian troops in Afghanistan, and charged with being an accessory to the murder of his ex-wife in April 2013.

He was also facing more than 40 indecent and sexual assault charges, which he denied, and was due in court in February.

His former lawyer, Manny Conditsis, told the BBC that Monis seemed to have become "unhinged" during the past year. Anne Davies, a journalist who met him at a rally in September, said the gunman had appeared "a little unstable...He also seemed a little creepy.

"Ominously, he also told me he did not think giving speeches would be enough," Davies added.

A statement signed by over 40 Muslim institutes, groups and associations was released yesterday condemning the incident in Sydney.

"We reject any attempt to take the innocent life of any human being, or to instil fear and terror into their hearts," the statement read.

"Any such despicable act only serves to play into the agendas of those who seek to destroy the goodwill of the people of Australia and to further damage, and ridicule the religion of Islam, and Australian Muslims throughout the country."

Jamal Riffi, described as a Muslim Community figure, told Australian media that Monis was acting alone. "The action of this man is the action of a madman and should not and is not reflected by the attitude among the Australian Muslim community," he said.

Concerns that Muslims would be afraid to travel around Sydney in religious attire for fear of Islamophobic attacks yesterday were met with offers of support and the hashtag #illridewithyou.

People tweeted their public transport schedules, and offered to travel with any Muslims fearing abuse. The hashtag trended globally.

Australian police locked down the centre of Sydney yesterday after Monis took a number of hostages in a Lindt café in the heart of the financial district.

The 16-hour siege ended in a police raid. Monis and two of his hostages – 34-year-old manager Tori Johnson and barrister Katrina Dawson – died.