A former member of the Australian military's elite domestic counter-terrorism unit has publicly questioned the choice of weapon used by police in last month's Sydney Lindt cafe siege.

Hostages Katrina Dawson and Tori Johnson and gunman Man Haron Monis died in the final moments of the December 16 siege.

Today a coronial inquiry into their deaths confirmed Ms Dawson died after being hit by fragments from a police bullet.

Mitchell McAlister, who spent two years as a tactical assaulter with 2nd Commando Tactical Assault Group, said he believed the threat posed by the lone gunman did not require a military counter-response.

But he said he had serious issues with the weapons used by the NSW Police Tactical Operations Unit (TOU).

He said he believed the choice of weapons have contributed to the death of Ms Dawson.

Writing in the American online journal SOFREP, a magazine presenting news and analysis from former special forces operatives, Mr McAlister said the same weapons would not have been used if the Federal Government had called in its own specialist elite counter-terrorism unit.

Mr McAlister is a former member of Tactical Assault Group - East (TAG-E), the Special Forces counter-terrorism unit based at Holsworthy Army base just west of Sydney, and within an hour's drive of the city's CBD.

TAG-E is part of the 4RAR commando unit set up to specifically deal with domestic counter-terrorism situations. The Tactical Assault Group was first established in response to the bombing outside the Hilton Hotel in Sydney in 1978 and became fully operational in 1980.

Mr McAlister noted that in nearly every image - apart from those of the snipers - police TOU operators were seen using M4A1 carbines.

He noted that the weapons fire heavy 5.56mm rounds that would have "dangerous effects in a dense and enclosed environment" such as the Lindt cafe. The cafe's interior is made entirely out of marble.

He said if his 2nd Commando regiment counter-terrorism team was used, they would have had a wider range of weapons to choose from that would have been more appropriate in the Lindt cafe situation.

"We specifically tailor our choice of weapons to the task at hand," he said.

Katrina Dawson and Tori Johnson died during the siege at Martin Place. ( Supplied )

"As a force element whose focus is specifically on resolving incidences through the use of force rather than negotiation, it is our duty to understand what weapons are suited to what environments.

"We are advanced weapons specialists and knowing the characteristics and effects of weapons, ammunition and explosives in different environments is an integral part of our trade.

"The siege was isolated to the confines of the Lindt Cafe, which had me wondering why a weapon system such as an M4A1 was favoured over, say, the H&K MP5 or H&K MP5 variants."

Mr McAlister said special operations units around the world who specialised in domestic counter-terrorism and hostage rescue had favoured specific weapons systems such as the MP5 in order to mitigate the damaging effects that higher powered rifles and their ammunition could generate.

The MP5 is a lightweight weapon designed for exclusive use in close personal protection and hostage recovery in close quarter combat environments such as buildings, aircraft and ships.

Mr McAlister clearly did not want to be overtly critical of the NSW police operation, and said: "It was their incident and they managed it accordingly ... the police did an outstanding job and should be commended for their efforts."

He said he could "understand the choice to go M4A1 heavy if the event was, say, an active shooter, or there was the potential for a weapons overmatch (such as in France where the terrorists used Kalashnikovs), but it was a hostage scenario with one individual in a confined space armed with a shotgun."

In his article, written before today's inquest hearing, he noted that some media had been reporting that it was a police ricochet that killed Ms Dawson.