British police say the driver of a tram that derailed in London, killing seven people, has been released on bail.

The 42-year-old man, who has not been publicly named, was arrested after the crash on suspicion of manslaughter. British Transport Police said Thursday he had been bailed until May while the investigation continues.

The tram came off the rails while rounding a tight curve in south London's Croydon area early Wednesday. Seven people were killed and more than 50 injured.

Emergency workers labored for hours to free several people trapped in the wreckage.

Accident investigators say the tram appears to have been "traveling at a significantly higher speed" than the permitted 12 miles per hour (20 kph). One theory under investigation is whether the driver fell asleep.