(CNN)A snow leopard was shot and killed at a zoo in the United Kingdom after it escaped an enclosure left open by its keeper, zoo officials said.
The revelation Friday that Margaash, an 8-year-old snow leopard, was shot dead October 23, after the zoo had closed to visitors, prompted dismay among conservationists. The species is considered vulnerable to becoming endangered.
"This was an incredibly sad incident and our staff are understandably heartbroken," Dudley Zoological Gardens Director Derek Grove said in a statement.
"Euthanasia is, and always will be, a last resort," he said. "Efforts to persuade Margaash to return to his enclosure failed and as the animal was close to surrounding woodland and dark was approaching, the vet did not believe a tranquillizer dart was a safe option due to the amount of time the drug takes to work."
Zoo staff had "no other option in the interest of public safety," according to the statement, adding that the animal "did not suffer" as it was euthanized with a single shot by a senior member of the firearms team.
The zoo's focus since the incident "has been to fully investigate what happened and carry out a stringent review of all zoo enclosure security," according to the statement.
The Snow Leopard Trust noted that snow leopards remain under severe threat and are classified as vulnerable by the International Union for Conservation of Nature, which means the species faces a real danger of extinction, spokesman Matt Fiechter told CNN.
While it's hard to pinpoint the species' global population, the Snow Leopard Trust estimates that only between 4,000 and 6,500 animals remain in the wild, he said. The global zoo population of snow leopards stands around 500.
Dudley Metropolitan Borough Council was "hugely saddened" by the news of the snow leopard's death but supports the zoo's handling of the incident, said Cathryn Bayton, a local politician responsible for public health.
"We fully support the actions they took and will be working with them, offering support and advice following this most unfortunate incident, and have every faith in their ability to deliver on the terms of their license," she told CNN.
Margaash arrived in 2011 at Dudley Zoo, in the English West Midlands, from Banham Zoo, in the east of England, and lived with a 3-year-old female named Taïga.