The president of a Florida zoo defended Thursday the decision to tranquilize and not kill a rare Malayan tiger that had fatally attacked a keeper and was preventing rescuers from giving her aid.

Palm Beach Zoo President Andrew Aiken told a news conference rescuers feared a bullet could ricochet off the steel and concrete enclosure and strike keeper Stacey Konwiser, whom the 13-year-old male animal was standing over after the April 15 attack. Aiken also said if the bullet didn't instantly kill the animal, he may have become enraged and attacked the veteran keeper again. It took about six minutes for police and paramedics to arrive after the 911 call from the zoo, five minutes to shoot the tiger with the tranquilizer dart and five minutes for the animal to be fully sedated.

Konwiser, 38, was taken to the hospital, where she died of a neck injury. Aiken said she had no pulse when rescuers reached her inside the pen.

Aiken criticized speculation that the zoo hesitated to kill the animal because it is only one of about 250 Malayan tigers left in the world. The zoo has four -- three males and a female.

"We place our employees' lives and their well-being first always," he said. "The fact the animal is endangered played no role in the decision making process. The decision to use a tranquilizer dart instead of shooting the animal was made during a crisis situation using the best information available to us at the time. To be clear, if this was the last animal of its kind and a human life was in danger, we would kill the animal."

Konwiser had worked at the Palm Beach Zoo for three years after working at the Palm Springs, California, zoo.

The attack happened in the tigers' night house, an area where they eat and sleep and is not part of the public exhibit. Aiken said it may never be known why Konwiser entered a part of the night house where she knew a tiger was present — she and her partner had placed the animal there that morning and had set the warning sign on the door. She also did not radio her partner to say she was entering the enclosure, as was protocol. He said it is unknown whether Konwiser had not radioed her partner on previous occasions when she entered the night house.

No cameras were operating in the area. Aiken said they are only used to monitor breeding efforts, so were turned off during the attack.

Aiken said Konwiser had given notice that she had accepted a job with the Food and Drug Administration, but he said the zoo had offered to match her salary and give her new responsibilities in an effort to keep her. She had not given a decision. Her husband, Jeremy, is a Palm Beach Zoo employee.

The investigation into Konwiser's death is being carried out by West Palm Beach police, Florida Fish and Wildlife officials and by federal authorities with the Occupational Safety and Health Administration.