Though euthanizing captive whales is rare, a number of the 5,000 marine mammals that find themselves stranded on U.S. beaches every year are killed, said Janet Whaley, a vet at the National Oceanic and Atmospheric Administration's fisheries department.
In the United States, beached whales are typically euthanized using a chemical cocktail, but they are simply shot in other countries, she said.
By some accounts, Tillikum was depressed and acting erratically, but Chuck Tompkins, curator of zoological operations at SeaWorld Orlando, told "Good Morning America" that the whale was "a good animal."
Tompkins said the whale attack may have been triggered by Brancheau's long hair, which swatted the whale in the face and by which the animal grabbed the trainer.
"What we have found out is that Dawn [Brancheau] had just finished up a very good session with this animal. ... She was interacting with him, petting him on the nose," he said." "Dawn had very long hair in a ponytail. That ponytail had swung in front of him. He grabbed her by the hair and pulled her underwater and held her underwater."
Eyewitnesses watched through an underwater window as the whale thrashed and drowned its trainer.
"We thought it was part of the act," said tourist Wayne Gillespie, who was at the killer whale show with his wife and two children. "We thought maybe they were playing together until we realized he was thrashing around pretty hard. That's how we knew something was wrong."