A witness told CNN affiliate WKMG-TV that the whale approached the glass side of the 35-foot-deep tank at Shamu Stadium, jumped up and grabbed the trainer by the waist, shaking her so violently that her shoe came off. A SeaWorld employee, who asked not to be identified, also described the incident the same way.
The whale's name is Tillikum, the SeaWorld employee said. The same whale has been linked previously to two other deaths.
"One of our most experience animal trainers drowned" in the accident, said Dan Brown, vice president and general manager of SeaWorld Orlando.
"We'll make our findings known in due course," he said. "We've never in the history of our parks experienced an incident like this. All standard operating procedures will be reviewed."
"During the show, everything was perfectly fine," she told CNN.
Afterward, "we went down to look at his full body underneath the isolation tank," she said. "Everything seemed calm and OK. The trainer was laying down on him and kissing his nose and rubbing him."
But the scene changed quickly, she said.
Jeffrey Ventre, a former SeaWorld trainer, described Brancheau as "a great trainer" and Tillikum as "a great animal" who has sired some 13 offspring.
"He's huge, he's impressive; people just see him and they go 'Wow!' He's a money stream as well."
Fred Felleman, a marine consultant in Seattle, Washington, said keeping the social animals in what amounts to isolation is bound to cause problems.
"What happened is something that happens; it happens in our line of work," he said. "They are dangerous animals; they're wild animals."
He added that he hopes SeaWorld continues with the work it does with killer whales.
But a spokesman for People for the Ethical Treatment of Animals called the death "a tragedy that didn't have to happen."
Jaime Zalac said the organization had called on SeaWorld "to stop confining oceangoing mammals to an area that to them is like the size of a bathtub, and we have also been asking the park to stop forcing the animals to perform silly tricks over and over again. It's not surprising when these huge, smart animals lash out."
The 11,000-pound, 22-foot-long whale was "not accustomed to people being in his tank" and "wouldn't have realized he was dealing with a very fragile human being," Solomons said at the time.
"He may have been a victim of what a whale would call horseplay -- just playing around," Solomons said.
Tillikum and two other whales also were involved in the drowning of a trainer at a Victoria, British Columbia, marine park in 1991.