Story highlights Tram driver is released on bail after his arrest on suspicion of manslaughter

Police will assess how and when to move the derailed tram from the tracks

London (CNN) Police continued Thursday to investigate the site of a tram derailment in Croydon, south London, that killed at least seven people.

The tram's driver, a 42-year-old man, was released on police bail early Thursday after being arrested following the crash on suspicion of manslaughter. He has not been named by the British Transport Police.

More than 50 people needed hospital treatment after the incident to the east of Croydon, a large town of about 38,000 people.

Emergency responders look at the overturned tram in Croydon, south London, on Wednesday.

Deputy Chief Constable Adrian Hanstock said Wednesday officers who arrived on the scene shortly afterward "were met with a complex and challenging situation."

He added: "This is a tragic incident and our hearts and thoughts go out to all those affected."

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