The incident took place at South Lakes Wild Animal Park in northwest England's Cubria Friday.
According to the park's owner, David Gill, Sarah McClay, 24, was very experienced in handling big cats. But for some unknown reason, the 24-year-old entered the tiger's enclosure Friday breaking the park's strict safety protocols.
"For some unknown reason, an inexplicable reason, because there is no reason for why she did it, she opened the door and went into the tiger enclosure and straight into the tigers, and now we'll never know why," said Gill who heard the attack and raced to the enclosure.
McClay was rushed to the hospital but later succumbed to her injuries.
The investigation is ongoing. No word on whether the tiger will be put down has been released. The tiger has been locked in its enclosure since the attack.
The Associated Press contributed to this report.