London ? A marine mammal expert conducted a necropsy Sunday on the whale that wandered into the River Thames, hoping to determine what caused the 20-foot-long animal to veer off course and splash through central London before dying during Saturday’s rescue attempt.

The Zoological Society of London said it hoped preliminary results on what killed the Northern bottlenose whale would be available Wednesday. Paul Jepson, who has conducted government-funded research into why dolphins and whales strand themselves on British shores, was performing the examination, the society said.

The whale captivated onlookers as it swam in the shallow, murky waters of the River Thames past the Houses of Parliament and Big Ben. It died Saturday night after rescuers tried to carry it into deeper waters of the North Sea.

Earlier, the whale twice tried to beach itself. Experts said the whale died Saturday after suffering convulsions and struggling with the effects of being out of the water.

The Zoological Society said Jepson would look for signs of damage to the whale’s skin before sending blubber samples for analysis. He would then examine the whale’s internal organs and the echo response areas of the brain, which may reveal why the mammal became lost.