Zoo officials have temporarily removed the large cats from public display and put a steel plate over the window smashed by a 450-pound Siberian tiger in the fatal attack of a zoo keeper.

Ricardo Tovar, 59, apparently was looking through a window in a door that led from the keeper's area to the exhibit grounds in the new $6 million cat habitat Thursday when Miguel, one of the zoo's three rare Siberian tigers, attacked.The cat shattered the glass, grabbed Tovar by the neck and dragged him into the outdoor habitat. Tovar died from a broken neck and crushed chest. The incident was the first fatal animal attack in the zoo's history.

Miguel, one of an estimated 400 Siberian tigers in captivity, will be kept in isolation until the investigation and safety measures are completed, said Donald Olson, director of the city parks department.

Security was intensified Saturday because of threats against the animal's life, Olson said, adding zoo attendance has not been affected by the mauling. Officials have no plans to transfer the cat to another facility.

Following the attack, zoo director John Werler described 11-year-old Miguel as "an aggressive cat."

"He snarls and growls," Werler said. "We have some cats that do neither of these things. Some are very placid."

Zoo employees wearing black armbands in memory of Tovar removed the rest of the large cats from public display Friday for an undetermined length of time.

"We're leaving them off display to let things settle down," Olson said, adding he would decide Monday whether to return them to the exhibit areas or leave them in their holding cages.

The tiger pounced through an 18-by-24-inch window in a door that led from the zoo keeper's area to the exhibit grounds. Zoo officials plan to put steel plates over similar windows elsewhere in the cat exhibit.

"Obviously it was not strong enough to hold the cat out," Olson said.

Olson was unable to explain why a wire-reinforced glass panel was used in the door panel of the exhibit that opened in November instead of heat-strengthened tempered glass, the usual choice of zoo officials who must contain large animals.