The driver of a tram that derailed killing at least seven people has been questioned by police amid suggestions it failed to break before taking a corner at speed.
The 42-year-old man from Beckenham has been bailed until May while investigations continue.
Investigators said the vehicle was travelling at a "significantly higher speed than is permitted" and are probing whether the driver may have fallen asleep.
More than 50 people were taken to hospital when the tram derailed and flipped on its side as it travelled through Croydon during the morning rush hour on Wednesday.
London Mayor Sadiq Khan warned the death toll "may well increase" after he visited the crash site.
British Transport Police (BTP) said investigators will remain at the scene until Thursday evening at the earliest, adding that identifying the dead may be a "complex and lengthy process".
Scenes in the wake of the crash were described as "total carnage" and "like something out of a film" after the two-carriage tram tipped over in heavy rain next to an underpass, as it travelled from new Addington to Wimbledon via Croydon.
Survivors rescued from the wreckage said they recalled the tram failing to brake in its usual place at a bend on the track after speeding up. One said the driver told them he thought he had "blacked out".
- On Wednesday Transport Secretary Chris Grayling paid tribute to the victims of the crash
Royal Navy veteran Kevin Snow, 57, was on his way to work in central London when the busy service overturned.
The father-of-seven from Barnsley, south Yorkshire, said the service, which he had been using regularly while working in London, failed to slow down at its usual point coming out of a tunnel between the Lloyd Park and Sandilands stops.
"Usually as you come out the tunnel you feel the brakes, but I didn't seem to at all. I thought, he should be braking in a minute," said Mr Snow.
"The next thing I knew we were on our side. Everyone was screaming and shouting, a lot of people were injured - lots couldn't move."
He said the tram slid for between eight and 10 seconds before coming to a halt.