MELBOURNE, Australia — Last month, at the Sea World amusement park in Florida, a whale grabbed a trainer, Dawn Brancheau, pulled her under water, and thrashed about with her. By the time rescuers arrived, Brancheau was dead.

The death of the trainer is a tragedy, and one can only have sympathy for her family. But the incident raises broader questions: Was the attack deliberate? Did the whale, an orca named Tilikum and nicknamed Tilly, act out of stress at being held captive in a sterile concrete tank? Was he tired of being forced to perform to amuse the crowds? Is it right to keep such large animals in close confinement?

Tilly had been involved in two previous human deaths. In one episode, a trainer fell into the pool and Tilly and two other whales drowned him. In another, a man who appears to have gotten into the enclosure at night, when Sea World was closed, was found dead in the pool with Tilly. An autopsy showed that he had a bite mark. One of Tilly's offspring, sold to an amusement park in Spain, has also killed a trainer, as have orcas in other parks.