An expert is carrying out a post-mortem examination on a whale which died after becoming stranded in the River Thames.
Despite a seven hour rescue attempt, the 18ft (5m) northern bottle-nosed whale died on a barge which was trying to take it back to deep waters.
The mammal suffered breathing problems and muscle spasms when it convulsed and died on Saturday evening.
Paul Jepson, from the Zoological Society of London, hopes to find out why the animal became lost on Friday.
Thousands of onlookers lined the river to watch as the mammal was put on a special pontoon at Battersea Bridge and then onto a barge on Saturday.
Plan scaled down
Millions more around the world then watched the doomed rescue attempt on television.
The whale was being taken to Shivering Sands off the north Kent coast, where rescuers had hoped to release it back into the sea.
This plan had already been scaled down from an earlier one to transfer it to an "ocean-going vessel" and take it to deep water off the south coast.
Rescuers tried to keep the whale cool as they moved it by barge
Earlier, naturalist and television presenter Terry Nutkins said the rescue operation was the wrong thing to do and that the animal needed space.
He told BBC Radio Five Live: "It wouldn't know what was happening, it was surrounded by boats... it would have been absolutely terrified as well as being stressed.
"It was kept... like a goldfish in a bowl. So, it doesn't surprise me that it's died."
However, he later concluded he had "no doubts" the rescue operation had been the best way to try to save the whale.
Tony Woodley, a director of the British Divers Marine Life Rescue (BDMLR) group said that despite the sad outcome, the decision to move the whale - costing the group about £100,000 - was correct and they had given it their "best shot".
He said: "The organisation was under extreme pressure from other experts and the media and it is our opinion that we did the right thing for the whale.
"We believe that if the whale would have been left how it was then it would have just slowly died and we don't think that was the acceptable option to take.
"We always knew that it was going to be risky. We did everything that we could and I am afraid that this time it was not a success."
He denied suggestions that the noise made by boats as the whale lay in the Thames caused its eventual death.
A spokeswoman for the Zoological Society of London said Mr Jepson was among the best qualified to carry out the post-mortem examination given his previous research work on stranded marine mammals.
It will be carried out at Gravesend in Kent where the whale was unloaded and take about six hours.
She added the results of the tests would be known on Wednesday or Thursday.
The whale, which could weigh about four tonnes, was first spotted at on Friday morning.
There were reports of a pod of whales in the Thames estuary earlier in the week, and it was possible the whale had become separated from this group.
It was the first sighting of the endangered species in the Thames since records began in 1913.