An engineer who approved the plans for a stage that collapsed before a Radiohead concert in Toronto says the drawings contained "very sloppy" mistakes.

Domenic Cugliari is testifying at a coroner's inquest into the death of Scott Johnson, a drum technician who was killed when the structure came crashing down just hours before the show was set to start on June 16, 2012.

Cugliari says the stage plans didn't spell out how to attach beams to the trusses in the roof grid and included "conceptual drawings" that should not have been submitted to the contractor. He says there were also inconsistencies that would likely have been caught if another engineer had reviewed the documents.

Cugliari, contractor Optex Staging and the show's promoter, Live Nation, were charged under provincial health and safety laws in connection with the incident but the case was halted because it took too long to get to trial. The case was thrown off course when the presiding judge was appointed to a higher court, prompting another judge to declare a mistrial.

The court eventually agreed with the defence that the delays had violated the accused's rights to a timely trial.