Lion Attack at California's Cat Haven Under Investigation

Tonight, authorities are trying to solve the mystery at a wild life sanctuary in california. A young woman inside one of the cages with a lion, the lion attacked and killed her. Abc's cecilia vega now... See More

Tonight, authorities are trying to solve the mystery at a wild life sanctuary in california. A young woman inside one of the cages with a lion, the lion attacked and killed her. Abc's cecilia vega now with the latest. Reporter: Cute and cuddly, couscous was irresistible as a 3-month-old cub. Can I hold him? Reporter: Four years and 500 pounds later, couscous, raised almost entirely in captivity, turned on 24-year-old intern dianna hanson. The person is still in the enclosure with the lion. Ems will be holding back. Reporter: Something caused couscous to go on the attack, the lion broke the intern's neck, killing her instantly. It then scratched and bit her entire body. It with us hanson's dream job. Her job was to work with big cats all day long. Feed them, taking care of them, playing with them. It was her dream. Reporter: But on wednesday, her father's worst fear came true. The only other worker at the park frantically tried to distract the lion as it mauled hanson, but there was no saving her. Sheriff's deputies say they had no choice. To get to hanson, they had to shoot and kill couscous. And the lion has been taken care of. Amazing. Incredible predators. Reporter: How could this same cat turn from a gentle cub nursing a bottle on ellen's lap to a full-grown killer? Veteran zoo keeper jack hanna says even wild animals raised by humans should not be treated as tame. At his zoo, trainers do not go in the cages of most big cats older than 8 months. Beautiful young lady crossed in the comfort zone of the lion. Number one, set off alarm, in my brain right away. Why would she be in there by herself? Reporter: Sometimes it's unclear what makes an animal turn on the very people who raised them. Siegfried & roy lived with their tigers but one day, one of those big cats turned on roy, nearly killing him and no one knows why. In the case of hanson, she had only been on the job for two months. She loved that lion. Loved that tiger. She was disappointed they wouldn't let her in the cage, because the rules were, only the owner could go into the cage. Reporter: But couscous had already become one of her favorite cats. Cecilia vega, abc news, los angeles.