Two bolts were missing from the structure that collapsed on the M1 in Sandton, killing two people and injuring 19 others in October.This was revealed in Johannesburg yesterday during the Department of Labour's commission of inquiry into the collapse of the temporary structure, part of a project to build a pedestrian and bicycle bridge over the highway.But it is yet to be established whether this was what led to the collapse of the structure. Yesterday two companies working on the structure could not agree on who was responsible for its design.Commissioner Lennie Samuel, the department's forensic investigator, called on affected parties to explain their involvement in the construction.Murray & Roberts, the main contractor , told the inquiry it was responsible for erecting the now collapsed temporary structure, including scaffolding and super beams.The temporary structure, to be used to support construction work on the permanent bridge, would be removed from the site once the construction had been completed.But the firm's legal representative, Richard Hoal, said Form-Scaff, a firm Murray & Roberts had subcontracted, was responsible for the temporary structure's design.Form-Scaff denied this, saying it only provided the material but did not design the structure.Its legal counsel, advocate Ewan Rudolph, said Form-Scaff would not have agreed to take responsibility for the design or the construction because it did not have an engineer in its employ.Rudolph said Form-Scaff had liaised regularly with Murray & Roberts engineer Roger Barker, who had assumed responsibility for the design, inspection and approval of the temporary structure.He also said shortly before construction Form-Scaff raised concerns that the site was not properly prepared for its delivery of the construction materials.Johannesburg Development Agency senior development manager Siyabonga Genu told the inquiry it was responsible for the project in its entirety and employed Murray & Roberts to carry out all the construction work, engineering firm Royal HaskoningDHV to prepare the bridge's specification drawings and Nemai Consulting to ensure that safety and health standards were met.Ian Green, for Royal HaskoningDHV, said it had handed the construction site over to Murray & Roberts in January 2015.Genu said it was found at a meeting following the collapse that two bolts were missing in the structure. But none of the parties could provide a reason for the fatal collapse.The parties have until the end of next month to submit final investigative reports before the hearings continue in April...