Police and paramedics who responded to the Hilton Hotel bombing in Sydney 40 years ago have joined victims' relatives at an emotional service marking the anniversary of the attack.
The bomb, hidden inside a bin, was loaded into a rubbish truck on February 13, 1978, detonating when it was crushed.
It was Australia's first experience of domestic terrorism.
Garbage collectors Alec Carter, 37, and William Favell, 36, were killed in the blast and police officer Paul Burmistriw, 31, died from his injuries nine days later.
While the intended target was believed to have been then-prime minister Malcolm Fraser and 11 visiting heads of state - in Australia for the first Commonwealth Heads of Government Regional Meeting (CHOGRM) - the culprit remains a mystery.
Relatives of the victims and former paramedics and police gathered at the Hilton in the CBD on Tuesday to remember their loved ones.
Retired chief inspector Gary Raymond recalled being called to the scene and having little information about the explosion's source.
The last thing on his mind was that it may have been a terrorist attack, Mr Raymond said.
"It doesn't matter what service it is, when you see members down you just go cold," he told the crowd.
Mr Raymond recalled how the "enormous force" of the bomb overwhelmed emergency services personnel.
"From a police point of view, this was a murder," he said.
Police Minister Troy Grant spoke of the "complete shock and utter grief" that followed the bombing.
It was described at the time as "a black day for Australian freedom", Mr Grant said.
The service included a presentation of photographs showing the severely damaged garbage truck, debris strewn across the Sydney CBD road and paramedics working on the injured.
Opposition leader Luke Foley paid tribute to the victims' family members.
"Our act of commemoration each year can never be enough, it can never bring back that you lost," Mr Foley said.
In addition to the fatalities, 12 people were injured in the attack.
A wreath will also be laid outside the Hilton on George Street to mark the anniversary.