The director of Alan Reay Consulting, the structural engineering firm that designed the Canterbury Television Building, came under intense questioning on Monday about documents missing from evidence his firm submitted to the Canterbury Earthquakes Royal Commission.
The commission is looking into the collapse of the office block in which 115 people died in the February 2011 quake.
Alan Reay said he submitted printed copies of information about the building held on computer discs, and had since destroyed the originals.
Under cross-examination from the families' lawyer, Mr Reay said the firm transferred all of the information from the discs onto a computer hard drive and did not see a need to keep the discs.
He was also asked why he felt qualified to give evidence about the building's collapse that didn't relate to its design, when he had no calculations to back it up.
Mr Reay said his evidence, which suggested five possible reasons for the collapse, was not intended to shift the blame away from his firm.
He also said he was not being selective about issues to be investigated in order to avoid taking any blame for the building's collapse.
He said his company instigated a test that proved the concrete used in the construction was not a cause of the collapse.
Mr Reay said the concrete manufacturer could have been blamed had the test not been done.
Last week Mr Reay told the inquiry he accepted his firm was responsible for any deficiencies in the design of the building.