“We have charged one person because we have reasonable grounds for suspicion. The man we have charged has a role we would like to look at more closely,” prosecutor Hildefunn Mikkels told newspaper VG.
She underlined the importance for the police of a broad probe that would enable them to explore several lines of investigation.
The investigation has so far indicated that the crash resulted from human error rather than any fault with the train.
A report from the Accident Investigation Board Norway (AIBN) showed that the train was travelling at almost twice the speed limit at the time of the accident.
All five people on board were injured, none of them seriously, when the train derailed on a stretch of track between Nykirke and Holmstrand, south of Oslo. Having come off the rails, the train smashed into a telephone mast and a bank of rock.
The train was travelling at a speed of 135 kilometres per hour when the brakes were applied. The speed limit on that section of the track was 70 kilometres per hour, AIBN said.
The train was part of rail operator NSB's new Flirt (Fast Light Innovative Regional Train) fleet, a model made by Swiss firm Stadler. The new trains had been scheduled to start running on regional and local networks across Norway from February 29th but the start date was postponed indefinitely after Wednesday’s accident.
NSB has ordered 50 Flirt trains from Stadler at a cost of 4.2 billion kroner ($730 million). The Norwegian operator also has an option to buy a further 100 trains.
Flirt trains can reach a maximum speed of 200 kilometres per hour.