A task force looking into why a giant video panel fell at a MIRROR concert last month said one of the cables that was used to secure the panel had quality and operational issues.

Speaking to the media after holding their fourth meeting on Wednesday, the task force's expert advisor Eric Lim said they believe the cable broke because of metal fatigue after inspecting it using a 5,000X microscope.

He said the steel wires of the cable were 20 percent weaker than normal, and some unstressed wires were damaged.

Lim added the cable was under extra pressure during operation because a part of the machine called "rope guard" – to help keep the rope steady – was not working properly, and the weight of the panel was much heavier than what the concert organiser had declared.

All of these factors, he said, contributed to metal fatigue within a short period of time, causing the cable to snap.

Lim added that it is difficult to say whether human error was involved.

The chairman of the task force, Lee Tsz-chun, echoed his views. "It's still under investigation and also the police and the Labour Department are conducting an investigation on their own, so I don't think we should give any comment on who should be responsible for the incident," said Lee, who's also assistant director of the Leisure and Cultural Services Department.

Lim added their probe would continue, saying they had yet to find out why the eyebolt of another cable holding up the panel broke. He said they hope to wrap up the investigation in September.

Two dancers were hit by the falling giant video panel at Hong Kong Coliseum on July 28. One of them, Li Kai-yin, suffered cervical vertebrae damage.