A witness has told a court the man accused of causing the death of Allan Hubbard was driving erratically before he collided with the Canterbury businessman's car in September 2011.
Andy Earl from Mosgiel, near Dunedin, has pleaded not guilty to charges of careless driving causing death and careless driving causing injury to Mr Hubbard's wife, Jean, who was in the driver's seat and suffered broken ribs.
Derek Gee on Tuesday told the Oamaru District Court, which is sitting in Timaru, he was travelling in front of Mr Earl on State Highway 1 before the collision.
Mr Gee said Mr Earl's red utility vehicle had been swerving unsafely and when it was about 300 or 400 metres behind him, he saw it cross fully over the centre line.
He said a few seconds later, the Hubbards' car braked heavily before colliding with Mr Earl's vehicle.
Mr Earl's lawyer, John Westgate, told the court another witness driving behind the Hubbards would say that their vehicle was straddling the centre line before the crash.
The hearing before Judge Gary MacAskill is expected to take three days.
Alan Hubbard was facing 50 fraud charges at the time of his death.