Police underestimated the threat posed by a self-styled Islamic cleric during a Sydney cafe siege and took too long to storm the building, an inquest found Wednesday, May 24, but it absolved them of blame for two deaths, AFP reveals.

The findings into the December 2014 tragedy that shocked the nation followed intense scrutiny of New South Wales police tactics, which have been blasted by families of those who died.

Despite his criticisms, coroner Michael Barnes made clear Iranian-born Man Haron Monis, a "vicious maniac", was solely responsible for what unfolded at the Lindt cafe in the city's financial hub.

"I cannot stress too heavily that the deaths and injuries that occurred as a result of the siege were not the fault of the police," he said. "All of the blame for those rests on the shoulders of Man Monis.

"He created the intensely dangerous situation. He maliciously executed Tori Johnson.

"He barricaded himself into a corner of the cafe and his actions forced police to enter the cafe in circumstances where the risk of hostages being wounded or killed was very high."

Monis, 50, began the siege in the upmarket chocolate cafe early on December 15, 2014, taking staff and customers hostage for 17 hours, armed with a pump-action shotgun.

It ended after he shot dead 34-year-old cafe manager Johnson.

Tactical police stormed the building, killing Monis while Katrina Dawson, a 38-year-old barrister and mother-of-three, died after being hit by a ricocheting police bullet or fragment.