A stage in Toronto’s Downsview Park, set for a Radiohead concert, collapses hours before the show June 16.

Sources told the CBC that staff from Upstaging, which did the lighting for the June 16 show, expressed concerns the stage was bearing too much weight. But an engineer from an undisclosed firm gave the OK, they said.

The Ministry of Labour’s investigation is expected to examine those claims and help determine whether those who operated and set up the structure were properly trained.

Live Nation, Radiohead’s Ticker Tape Touring and two Canadian companies – Optex Staging and Services and Nasco Staffing Solutions – have all been asked to comply with the investigation.

Radiohead drum tech Scott Johnson, 33, of Doncaster, England, was killed and another crewmember hospitalized with a non-life-threatening injury after the outdoor stage roof collapsed at 4 p.m. while crews were setting up for the concert. Two other people were injured and treated at the site.

Paramedics and firemen used inflatable airbags to lift the twisted wreckage to get to Johnson. He was pronounced dead at the scene of “heavy crushing injuries,” according to police.

The Live Nation-produced show was immediately canceled before admission gates were to be opened at 5 p.m. A crowd of around 40,000 was expected for the 7:30 p.m., sold-out show.

At the time of the collapse, the portable stage roof had already been raised into position with its full compliment of lighting gear. The band was only moments from taking the stage for soundcheck when the center section of the roof collapsed onto the deck without warning. It appears both of the front and one rear roof support connection failed.

Toronto was experiencing sunshine and blue skies when the stage failed, making weather an unlikely factor in the accident.

Radiohead has already distanced itself from the incident, asserting the band does not set up stages. A representative for the band said in a statement that “Radiohead installs its production into the performance space as provided by the venue and/or promoter,” the CBC reported.

A representative for Optex, which supplied the stage for the show, denied any knowledge of the event and refused to comment further when contacted by Pollstar.

And Live Nation, which promoted the show, has yet to offer much information beyond calling the incident a “serious and tragic accident.”

“This accident is being investigated but we do not have any further details at this time,” LN spokeswoman Liz Morentin said via email.

Live Nation has reporteldy been asked by the Ministry of Labour to produce an engineer-approved safety plan to disassemble what’s left of the stage. Officials from the agency have stressed the investigation could take some time.

“We’re still trying to figure out who owns what, who’s responsible for what,” Ministry spokesman Matt Blajer told the Toronto Star. “You’ve got lighting technicians, sound technicians, the band’s people – we’re trying to figure out who worked for whom.”

Next Media Animation Direct, a service that provides informative daily hard news animations, created the following video explaining what happened.

Toronto was the last date on Radiohead’s North American tour. The band’s next scheduled date is June 30 in Rome.