Ontario's Labour Ministry has identified four of the companies involved in setting up the outdoor stage that collapsed and killed a drum technician prior to a Radiohead concert planned for Saturday night in Toronto — including a business operated by the British band.

It also emerged Monday that the lighting crew for the show had hesitations about the amount of weight rigged up, but an engineer gave the OK.

The Labour Ministry said Monday a number of companies worked on the huge stage structure that fell apart, crushing a member of Radiohead's road crew and injuring three other people.

One of the companies was London-based Ticker Tape Touring LLP, which British corporation databases show is part of Radiohead's network of companies that manage the band's merchandise, tours, equipment, music distribution and publishing. The rock group's members make up the company board of directors, according to various databases.

The band's U.S. publicists said Monday that the band "is unable to comment concerning the stage structure at Downsview Park."

"Radiohead installs its production into the performance space as provided by the venue and/or promoter," an emailed statement said.

The Labour Ministry said it will also be talking to Toronto-based Optex Staging and Services Inc., the company that built the stage for Saturday's cancelled show. Optex has built stages and grandstands for many large-scale events, including the Edgefest and Lollapalooza festivals and shows by U2 and Bon Jovi.

Calls to the company on Monday were rebuffed. A woman who answered the phone said, "We're not going to comment. We don't know anything about it, so that's it. Bye."

Concert promoter Live Nation and Vancouver-based Nasco Staffing Solutions, which supplies technical crews for concerts and other major audio-visual events, were also involved in preparations for the Radiohead show, the Labour Ministry said.

Investigators have issued a number of orders to Live Nation, including a request for an engineer-approved plan to safely disassemble what's left of the collapsed stage in Downsview Park and a warning not to disturb the parts of the stage or the area around it once it has been dismantled.

The ministry has already been given the original, engineer-approved blueprints for the stage, but said it won't release the name of the engineering firm that signed off on it.

Live Nation would only say that "we do not have any further details at this time."

Lighting crew had qualms

Investigators are still trying to determine who was responsible for the faulty rigging and how it broke apart so calamitously on Saturday.

At about 4 p.m. that day, an hour before concertgoers were to be admitted for the outdoor show, the roof above the stage caved in. Radiohead drum technician Scott Johnson was crushed to death, while three other people were injured, one seriously.

Sources have told CBC News that staff from Upstaging Inc., the company hired to do lighting for the show, expressed concerns that the stage structure was bearing too much weight. But an engineer gave the OK, according to the sources, who spoke on condition of anonymity.

The ministry's probe will also look at whether the staff setting up and operating the stage equipment were properly trained.

Two experts say the tight deadlines faced by those crews might be a factor in Saturday's incident.

Radiohead is known for its extravagant light shows, and its North American tour that ended with the cancelled Toronto show was no different. Though the scaffolding for the Toronto stage was already up when the band arrived in Toronto from its concert the night before in Montreal, more than 4,500 kilograms of lighting and video equipment had to be installed in just a few hours on the stage ceiling.

"The thing that's unique about this type of facility is the speed that it goes up and the speed that it comes down. And it might very well be that the pace of the industry is just too fast to allow normal protocols to do their job," Toronto-based civil engineer David Bowick said.

Bowick added that temporary stages such as Radiohead's are inherently less robust. "Because of a lack of redundancy, a very small human error could precipitate a chain reaction."

Janet Sellery, a Stratford, Ont., safety consultant specializing in the arts, agreed that the pressure to produce flashy performances on a short turnaround could bear part of the blame. She also said inconsistent labour and safety standards are endangering those toiling behind the scenes at increasingly ambitious shows.

The full investigation into the disaster could take up to a year and could result in charges under the provincial Occupational Health and Safety Act. Toronto police have ruled out any criminal wrongdoing.