The family of Noleen Hayson Pal, the slain ex-wife of the Sydney siege gunman, have expressed their anger that he was not behind bars.

Man Haron Monis, 50, who was shot dead by police in the early hours of Tuesday morning, was on bail after being charged with being an accessory before and after the fact to the 2013 murder of Pal.

Pal's "god brother" Talat Khalik, who lives in California, posted a series of furious comments about Monis on Facebook.

"Thats systems tere f***d up but im still happy he.died [sic]," Mr Khalik, who refers to Pal as his sister, posted on his Facebook page.

"Fu**n lucky tey got u before we did now.rest in hell f****n asshole [sic]."

He also posted a picture of himself with his arm around Noleen, writing: "Noleen miss u [sic]".

His mother, Momina Khalik, who also lives in California, said Monis should have been in custody.

"y the first place they let him free on the sydney streets they should have let him rot in the jail his a f****n sick animal [sic]," she posted.

Pal, 30, was stabbed multiple times and set alight in a western Sydney unit block in April 2013.

Monis and his then partner, Amirah Droudis, were both charged over the murder but they were given bail on December 12 last year.

"It is a weak case," Magistrate William Pierce said at the time of the bail application.

Pal's godfather Ayuut Khalik said the first time he met Monis he didn't like him.

"They should have put him away and thrown away the key," he told NBC News.

"Who do you blame? The Australian government? The judicial system?" he said.

Mr Khalik said that Monis and Pal had two sons.

Monis, a self-styled sheik, made Pal wear a hijab and stopped her from contacting non-Muslims, he said.

"We found out he was hitting her and stuff, and he was telling his kids white people are bad."

Mr Khalik said when Pal came to stay with his family in California for a month last year he told her to be safe.

He said he found out Monis was involved in the hostage siege in Sydney when he received a Facebook message from a relative.

"It was like someone hit me with a sledgehammer," he told NBC News. "I just prayed for the hostages."