The only warning was a "loud, awful crack", before the concrete pouring boom that had been sweeping across the construction site fell fast and hard towards the scattering workers in hi-vis, a court has heard.
Ben Catanzariti, who started work with Belconnen Concrete three weeks earlier, died when the boom hit him that Saturday, July 21, 2012.
On Tuesday, nearly five years on, a long-awaited hearing into the 21-year-old concreter's death began in the ACT Coroners Court.
It is the job of Coroner Karen Fryar to investigate the cause of Mr Catanzariti's death, and identify and comment on any matters of public safety. She has the power to make recommendations for change.
Mr Catanzariti died when, as a concrete pour had just begun at the Kingston foreshore site, the boom fell and struck the back of his head. He suffered severe head trauma and a fractured skull.
Two other workers were also injured.
The focus of the coronial inquiry will be whether there were other factors that had contributed to Mr Catanzariti's death, and how they might be avoided in the future.
On Tuesday, the officer who investigated the death, Detective Senior Constable Simon Roscoe, detailed his findings to the court.
He said when the concrete pouring machine had arrived that morning, workers noticed it looked brand new. It had recently returned from manufacturer Schwing Australia Pty Ltd following a six-year inspection, and had been freshly painted.
The bolts had been removed and replaced during the inspection with new ones, which had been ordered by the concreting company from the US after some delays and trouble sourcing them.
But what went undetected on the day of Mr Catanzariti's death some three weeks later were the fatal weaknesses in the bolts securing the concrete pouring boom to the machine.
What caused the bolts to fail is an ongoing source of controversy, and one of the issues the inquest will consider.
Experts had provided three different opinions in three separate reports.
One expert, organised by ACT police shortly after the accident, said the bolts had failed because they had been incorrectly tightened by Schwing during the machine's maintenance.
Another expert, commissioned by Schwing, said the failure was due to a metallurgical phenomenon known as hydrogen embrittlement.
Another expert, organised by the ACT Director of Public Prosecutions, said it was a different phenomenon called stress corrosion cracking.
A fourth report, dated January this year and sought by Belconnen Concrete, said the failure was one of workmanship, and the bolts had not been uniformly tightened by Schwing.
The differing opinions had already caused the collapse of a criminal prosecution of Schwing and an engineer in 2012. The ACT Director of Public Prosecutions had to drop the case, after concluding the reports meant there was no reasonable prospect of conviction.
Counsel assisting the Coroner, Ken Archer, said at the outset on Tuesday any conclusion on the cause of the bolts' failures was "remote and unlikely". He suggested Ms Fryar accept each report, and if she found them to be true make recommendations based on each.
Questions over the machine's maintenance process were pressed at the inquest on Tuesday.
Senior Constable Roscoe agreed under questioning from Bernard Collaery, who is representing the young man's family, that there was nothing to suggest the boom had been load tested by Schwing employees before it was returned to the concreting company.
He said the three men who had been responsible for machine's maintenance had declined to speak to police. They had instead provided written statements in response to written questions under a workplace safety investigation, he said.
A second issue for the inquest is about exclusion zones around the boom: what zones had been put in place, whether there was compliance on the day, and what exclusion zones are appropriate.
The inquest was set down for a further two days this week.
However, a new report, as well as the identification of more relevant material, meant it has been put off to later this year.
The case is scheduled to return on September 28 and 29.
Correction: An earlier version of this article incorrectly said Belconnen Concrete was the subject of a criminal prosecution in relation to the worksite accident. Only Schwing Australia Pty Ltd and its engineer Phillip James O'Rourke were the subject of a criminal prosecution. That prosecution was withdrawn in 2012.