Network Rail says it will plead guilty to a series of health and safety offences following the fatal Grayrigg train crash in 2007.
Passenger Margaret Masson died and 86 others were injured when a Virgin Pendolino was de-railed in Cumbria.
The company will be sentenced next month.
Today Margaret Masson's son, George, said that his family had been through hell for the last five years.
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Sandy Murray, of Police Scotland, was was giving evidence at the trial of a bus driver who denies killing Ryan Baird by dangerous driving.
34-year-old Christopher Peck was involved in a head-on crash with a drunk driver. His funeral has taken place in his hometown, Workington.
The arrests come weeks after a much-publicised series of appeals to mark the 30th anniversary of the 18-year-old's death.