The radical self-styled Muslim Sheik Man Haron Monis behind the siege that saw 17 people held hostage in the Lindt cafe on Martin Place was a "damaged-goods individual" who could have lashed out because he felt he had "nothing to lose", his former lawyer says.

Monis, who was killed during the final minutes of the siege in Sydney's CBD, was no stranger to police; with a long rap sheet including allegations of sexual abuse and organising the murder of his ex-wife.

Monis was born Manteghi Bourjerdi and fled from Iran to Australia in 1996 where he changed his name to Man Haron Monis and assumed the title of Sheik Haron.

Lawyer Manny Conditsis, who represented Monis when he was charged last year with being accessory to the murder of ex-wife Noleen Hayson Pal, described the self-declared sheik as a "damaged-goods individual".

Sheik Man Haron Monis. (AAP) (AAP)

Sheik Man Haron Monis. (AAP) (AAP)

"His ideology is just so strong and so powerful that it clouds his vision for common sense and objectiveness," he told the ABC. "Knowing he was on bail for very serious offences, knowing that while he was in custody some terrible things happened to him, I thought he may consider that he's got nothing to lose."

"Hence participating in something as desperate and outrageous as this."

The self-styled sheik was shunned by Australia's Muslim community who disputed his claims of being a Sheik, according to community leader Dr Jamal Rifi

He had gained media attention in the past for a "hate mail" campaign, protesting the presence of Australian troops in Afghanistan by sending abusive letters to the loved ones of dead Australian servicemen.

Late last year he was charged with being an accessory to the murder of his ex-wife and mother of two.

More recently he was charged with a raft of offences in relation to indecent and sexual assault while operating as a self-proclaimed "spiritual healer" in Sydney's west more than a decade ago.

Mr Conditsis said Monis claimed to have been abused while in prison "involving matters of excrement over himself and his cell".

Sheik Man Haron Monis. (AAP) (AAP)

He added that he did not believe Monis was a member of any organised terrorist group.

"This is a one-off random individual," he said. "It's not a concerted terrorism event or act."

"It's a damaged-goods individual who's done something outrageous."

The High Court had recently rejected Monis' latest appeal in relation to letters he had sent to the families of Australian servicemen.

The family of Brett Till, an Australian solder killed by a roadside bomb in 2009, was one of the families who received a letter from Monis and his partner Amirah Droudis.

"We sat in our homes, reading these letters ... This man accusing my husband of being a child killer," widow Bree Till said at the time.

9NEWS was given police clearance to release Monis' name.

In November 2009 Monis appeared in court claiming to be a peace activist but later chained himself to the courthouse in protest of charges laid against him.

Monis escaped jail time but was sentenced to 300 hours of community service and placed on a two-year good behaviour bond in September 2013.

He again received attention from police in November last year when he allegedly organised the murder of his ex-wife and mother-of-two Noleen Hayson Pal.

Ms Pal had been stabbed and her body set alight in a Werrington apartment block, allegedly by Ms Droudis.

Monis was charged with being an accessory before and after the fact to the murder while Ms Droudis was charged with murder. The couple won bail in Penrith Local Court after a magistrate noted the prosecution case was weak, News Corp reports.

In April this year he was charged with sexually assaulting seven women while working as a spiritual healer in Wentworthville, where he claimed to be an expert in "astrology, numerology, meditation and black magic".

In October Monis, who most recently had been living at Bexley North in Sydney's south, was charged with an extra 40 sexual offences relating to his work as a spiritual healer.

He was on bail at the time of the siege and due to appear in court over indecent and sexual assault charges in February 2015.