At least four people died on Tuesday after a train from King's Cross, London, derailed near Hatfield in Hertfordshire.
Two of the train's eight carriages ended up wrecked on their sides after the 12.10 GNER service to Leeds left the tracks at more than 100mph.
There were around 20 serious injuries and 80 people were described as walking wounded.
Debris and wreckage was scattered over two lines of the track a short distance from Hatfield Station.
Investigators arrived at the scene on Tuesday evening and the area was designated a crime scene.
The British Transport Police and officials from the Railway Inspectorate will now work to determine the cause of the accident.