The psychiatrist who advised police negotiators during the Sydney siege says Man Haron Monis was seeking infamy rather than wanting to hurt people.

He said it became clear early into the stand-off that he was not affiliated with Islamic State.

But the psychiatrist, who for legal reasons cannot be identified, has told the inquest into the December 2014 siege that it could also never be discounted that Monis had a bomb in the cafe, prompting police to stick with their strategy of contain and negotiate.

While Islamic State had been calling for lone-wolf attacks in the lead-up to the siege at the Lindt Cafe, the gunman did not fit the classic profile.

The methodology employed during the stand-off did not match that which had previously been used by the extremist group, he told the inquest on Tuesday.

"It's all about absolutely confronting a peaceful community with (some sort of) atrocity in a very pointed way, whether it's running someone down in a car or stabbing them in the street or beheading somebody with a meat cleaver or whatever else some of these deranged people manage to do," he said.

"It certainly didn't involve putting people in a stronghold and talking for hours."

The psychiatrist, like others, said he formed the view early into the 17-hour siege that Monis had a narcissistic disorder.

He said it was "correct" that the gunman was intent on gaining notoriety rather than hurting people.

"This was a grandiose, self-focused event with scant regard for what was being done to other people to pursue an objective which was for the perpetrator's personal need to be recognised widely as a figure of great infamy," he said.

He said the methodology employed by Monis did not match that used by Islamic State, and the threat from the gunman that he had accomplices and bombs in other locations "made no sense", nor did his demand to debate former prime minister Tony Abbott on the radio.

"If one has gone as far as building bombs and you've built a terrorism cell where you have trusted people who are out there ready to detonate your bombs, to then ... say 'It's all right I've spoken to the prime minister you can take the bombs home now', that clearly was an implausible state of affairs."

Still, having come to his early conclusions, the psychiatrist said that police had to work on the basis that there was a bomb in the cafe.

"The bomb within the stronghold was never able to be discounted."

Police stormed the cafe after Monis shot dead manager Tori Johnson at 2.13am.

Monis was killed by police, while hostage Katrina Dawson died after being hit by police bullet fragments.

The inquest continues.