Former Transnet engineer Francis Callard will continue leading evidence at the state capture commission of inquiry on Monday.
Evidence presented last week revealed significant irregularities in contracts worth billions of rand.
Callard set out in technical detail why the China South Rail locomotives were not the ideal option for Transnet which needed trains to operate on the coal network.
He had argued that Mitsue was the better option because the company had already delivered products, which had been locally tested, prototyped and drivers had been trained.
The board, under the direction of group chief executive Brian Molefe, changed Callard’s memo to suggest it was in fact in favour of the Chinese manufacturer.
The engineer also revealed that Transnet and China South Rail had met prior to the proposal being formally issued, where technical specifications were discussed.
Callard is expected to provide further details on the purchase of 1,064 trains from the company.