Questions around evidence in M1 bridge collapse case

Presiding officer Lennie Samuel says Professor Roelf Mostert's evidence is based on assumption.

Two people were killed and 19 others injured when a temporary bridge over the M1 collapsed last year. Picture: Mia Lindeque/EWN.

PRETORIA - The presiding officer in the inquiry into the deadly M1 bridge collapse has raised concerns over the evidence of an expert testifying on behalf of Murray & Roberts, saying it's based on assumption and not fact.

Two people were killed and 19 others were injured when the temporary structure came crashing down on the busy highway last year.

WATCH: Bridge collapses on M1 in Johannesburg

The inquiry into the collapse is being held at Labour Department in Pretoria.

Murray & Roberts' first witness, Professor Roelf Mostert, gave evidence on the quality of material used in the construction of the bridge.

His evidence is now being closely scrutinised.

Mostert said while he could not say what exactly caused the steel scaffolding to cave in, he believed faulty couplers may have contributed.

"My brief was to investigate the mechanism of the collapse."

But presiding officer Lennie Samuel said the professor's evidence was based on assumption because the material he examined was not from the scene of the collapse.

"I need to actually base my findings on fact, not assumption, so I would like you to explain to me."

A second witness from Murray & Roberts is expected to give evidence when the inquiry resumes next week.