In short:

A steel fabrication company that provided the supports for a roof that collapsed at Curtin University's medical school in 2020, has admitted responsibility in court.

An apprentice carpenter was killed and several others injured in the incident.

What's next?

The company will be sentenced in October.

A company that provided steel supports for a roof that collapsed at Perth's Curtin University, killing a worker and injuring another, has admitted responsibility in court six years after the incident.

Apprentice carpenter Jonathan Hartshorn, 23, died in the 2020 roof collapse while Rikki Issitt suffered serious injuries which have prevented him from working.

Steel fabrication company Elsdon had pleaded guilty to failing to ensure workers' safety.

Perth Magistrates Court was shown two sets of CCTV footage of the incident, from different angles, with the two workers standing on the roof and then falling as it gave way.

The confronting video showed men running to the scene after the collapse.

Two other workers who were under the canopy were also injured.

The court heard that the welding for trusses was not done to specification, nor was it overseen by a qualified supervisor.

Emotional testimony

Mr Hartshorn and Mr Issitt were not directly employed by Elsdon at the university site, which was a Lendlease project.

Limping to the witness box, Mr Issitt told the court how he fell more than 20 metres, thinking he was going to die. He suffered multiple injuries, including to his spine and pelvis.

In an emotional statement, Mr Issitt said the accident had taken away his career and subjected him to years of almost constant pain and psychological distress.

Mr Hartshorn's mother Susan Chappell also read out a statement through tears, saying her son "had a right to go home at the end of that day".

She said he was a hardworking apprentice whose "future was torn from underneath him".

In a statement read to the court, Mr Hartshorn's partner, Kylie Galende, said she thought she was going to spend the rest of her life with him, but was now learning to live without him.

"He made me feel safe," her statement said. "And then in one moment he was gone."

Prosecutor Eric Heenan said the majority of the welds inspected after the incident had defects.

He told the court that Elsdon, in its defence, said it did not know it was sending inadequate welds to the site, but there had been "no procedures, no qualified welder, no supervisor, no test".

The maximum penalty under the legislation in force at the time is a $2 million fine.

Elsdon's lawyer Alex Mossop said the company accepted the welds at the trusses were meant to be "full penetration" and were not, and it did not know that its workshop "was not achieving".

Elsdon is due to be sentenced in October.

Stantec Australia, which was charged with failing to ensure the safety of workers, had both charges discontinued in May due to insufficient evidence, and had costs awarded.

The court heard separate civil proceedings had been initiated.