A snow leopard was shot dead after a zookeeper left the enclosure door open and it escaped.
Dudley Zoo said eight-year-old Margaash was killed after getting free on 23 October when the zoo had closed and all visitors had left.
An investigation found the door to the enclosure was left open at 17:00 BST through “keeper error”.
A disciplinary procedure has taken place into those involved and security is being reviewed.
Once keepers saw Margaash outside, the zoo said its animal escape procedure was put in place and the firearms team managed the incident.
The zoo said the leopard was killed by a senior member of the firearms team with a single shot and did not suffer.
It added staff had no other option and the decision was taken in the interest of public safety.
Zoo director Derek Grove said: “This was an incredibly sad incident and our staff are understandably heartbroken.
“Euthanasia is, and always will be, a last resort. 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 tranquiliser dart was a safe option due to the amount of time the drug takes to work.
“Safety of the public is always of paramount importance and our staff are highly experienced and rigorously trained.”
Snow leopards are endangered and there may be as few as 4,000 left in the wild
Estimates of their numbers in the wild are difficult because the animals are highly elusive
They are native to Central Asia
Its main prey are ibex, argali and bharal (Himalayan blue sheep)
Snow leopards measure between about 55 and 65cm (22 – 26in) tall and 90 to 115cm (36 – 44in) in length
They have been known to live for up to 22 years in captivity but in the wild their life expectancy is more like 10 to 12 years
The zoo said it had notified people who had “adopted” Margaash and had informed all the keepers so they could explain the situation to visitors.
Margaash was born at Banham Zoo in Norfolk in May 2010 and came to Dudley Zoo in September 2011, where he lived with its three-year-old female Taïga.