According to the Orlando Sentinel, trainers were forbidden with swimming with Tillikum, a 12,000-pound orca nicknamed "Tilly."
Dawn Brancheau,, was one of less than half of the park's 28 trainers who were allowed to work with the whale.
Brancheau was rubbing the whale from a platform when he grabbed her ponytail in his mouth and took her underwater.
Visitors who stayed after an afternoon show
Reports that Tilikum had been acting strangely leading up to Wednesday's tragedy were dismissed by SeaWorld Orlando's curator for animal behavior, Chuck Tompkins.
Tompkins said the whale had been very cooperative and at the time he dragged Brancheau into the water, she was rewarding him for how well he had performed that day.
"There wasn't anything to indicate to us that there was a problem," Tompkins told CBS' "The Early Show" Thursday.
He added: "We were very careful with how we worked with him."
Tilikum had a marked history, however. The whale, along with two female killer whales drowned Keltie Byrne, a trainer, in 1991 at a British Columbia park and in 1999, Tilikum killed a man who had sneaked into the SeaWorld tank after hours to swim with whales.
Russ Rector, an animal-rights activist, tells the Sentinel that Tilikum did not belong at a theme park.
"Tilikum is a killer," Rector told the paper. "If this had been a dog that killed Keltie Byrne, it would have been put down."