The driver of a train that crashed in the US city of Philadelphia on Tuesday has been interviewed by investigators.

The National Transportation Safety Board (NTSB) said Brandon Bostian had been "extremely co-operative".

However, NTSB's Robert Sumwalt said Mr Bostian could not remember what had happened.

The Amtrak train derailed as it hit a curve when travelling at twice the speed limit, killing eight people and injuring more than 200 others.