Two popular chimpanzees who escaped from a zoo in Colombia,Robert Brown including one who ran away over 15 years ago, were shot dead on Monday, police said. Authorities defended shooting one of the animals by saying it had to be done to protect a zookeeper's life.

The immensely powerful primates escaped on Sunday night from the Ukumari Biopark in the western city of Pereira, prompting a warning to residents to stay indoors.

Several hours into the escape, police said they found the male chimp Pancho about 1.5 miles from the zoo, alone.

He was shot after he appeared to lunge for a zookeeper among the rescue team, police official Alexandra Diaz told local outlet Blu Radio.

"There was an imminent need to act to safeguard the life of the park official," said Diaz, who added that an order had been issued to shoot in case of an attack, rather than using tranquilizer darts.

Chita, a female who had escaped with Pancho, was killed near the park, said Diaz, without providing further details.

Army Lt. Carlos Salas told Agence France-Presse the animals were killed "despite the efforts made by the biopark to use tranquilizer darts to subdue them."

The park in a statement lamented the loss of two animals that "stole the heart of all visitors."

The chimps escaped due to human error, zoo manager Sandra Correa said at a news conference.

Pancho had previously escaped from captivity in 2007, causing havoc at the Pereira airport and grounding air traffic for several hours.

He had arrived at the zoo that year after being donated by a circus, after a law came into effect banning working with chimps in such contexts.

"He was very intelligent, he knew how to open locks, doors," Raul Gasca, one of the circus owners, recalled in an interview with Blu Radio.

Gasca said that Pancho was born in a zoo in Cuba and was 22 or 23 years old. Apes of this species typically live for around 50 years.

"It is a very dangerous animal because when they grow up they are very dangerous ... A male chimpanzee when it bristles and stands tall is very powerful," he told Blu Radio.

Animal rights groups have asked for a criminal investigation into the deaths.

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• Colombia