The provincial Ministry of Labour has identified four companies involved in a stage collapse at Downsview Park that killed a Radiohead drum technician and injured three others.

Optex Staging and Services Inc., Nasco Staffing Solutions, Ticker Tape Touring LLP and Live Nation, the concert promoter, have all been asked to comply with an ongoing investigation into the June 16 accident, ministry spokesperson Matt Blajer confirmed to the Star.

While Blajer could not disclose specifics, he said the ministry has issued orders “mainly to Live Nation.” Stage blueprints signed and approved by a professional engineer have already been provided to investigators.

As three inspectors and two engineers from the ministry continued inspection at the scene Monday, Blajer stressed the investigation will “take time to unravel.”

The number of companies operating at the site remains unknown, posing a challenge to investigators.

“We’re still trying to figure out who owns what, who’s responsible for what,” Blajer said. “You’ve got lighting technicians, sound technicians, the band’s people — we’re trying to figure out who worked for whom.”

Representatives from Nasco and Optex, both of whom have Toronto offices, and Ticker Tape Touring could not be reached for comment Monday afternoon.

In a statement Monday, Live Nation expressed its condolences for the Radiohead drum technician, 33-year-old Scott Johnson.

“This accident is being investigated but we do not have any further details at this time,” said spokesperson Liz Morentin. “Our thoughts and prayers go out to Mr. Johnson’s family and friends and to the Radiohead family.”

Optex, a stage installation company, often hires extra labour from a staffing company, such as Nasco, for larger events. The company has provided staging for acts such as Pearl Jam, Van Halen and Bette Midler, according to its website.

Roughly 40,000 fans were expected to attend Saturday’s sold-out concert, which was cancelled almost immediately after the stage collapse.