The two men died when the passenger train left the rails and collided with the walls of a bridge near Greenock, Strathclyde on Saturday night.
Paul Prescott, Railtrack's director in Scotland, asked if there were any other possible causes besides vandalism yesterday, replied: 'None that I want to put forward.'
He said there had been 'one or two incidents' of vandalism in the area and confirmed that 'materials' had been found on the track at the crash scene.
A Strathclyde police spokesman said last night that the deaths were being treated as murder.
The accident happened shortly after 11pm when the 22.45pm Wemyss Bay to Glasgow service became derailed before colliding with the bridge at Peat Road, Greenock.
Arthur McKee, 35, the train driver of Baillieston, Glasgow, and Alan Nicol, 21, a student of Greenock, were both killed.
Mr McKee, a driver with 10 years' experience was married with a young child. Mr Nicol was engaged to be married.
Three passengers and a Scotrail guard were taken to Inverclyde Royal Hospital, Greenock, but released after treatment for shock.