Two monkeys are believed to have been taken from the Dallas Zoo following a series of bizarre events at the attraction.
Dallas police said there were no arrests in any of the investigations — which also included the hacking of a cage and the suspicious death of an endangered bird — and did not confirm whether the incidents were connected.
In one recent case, officials believed someone had opened a hole in a fence and taken two emperor marmosets, small primates with long beards that resemble beards.
“It is clear that the habitat has been intentionally destroyed,” the zoo said in a statement.
Earlier this month, the zoo was closed for a one-day search when Clouded Leopard Nova is missing.
She was eventually found near her roost, but police said tools were used to cut an opening in her fence.
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A similar opening was found in the langur enclosure, but none came out.
A week later, a critically endangered bald eagle named Pin was found dead, and the zoo said the death did not appear to be natural.
The zoo’s chief executive, Gregg Hudson, said the vulture was found with wounds.
Ed Hanson, chief executive of the American Association of Zoo Keepers, said he can’t recall a single zoo dealing with so many similar incidents with such frequency.
“It looks like someone really has a problem with the Dallas Zoo,” he said.
Mr. Hanson described the Dallas Zoo’s reputation as “excellent” in the industry, adding that certified zoos have double-walled fencing and that a zoo as large as Dallas has security patrols.
The Dallas Zoo said in a statement that it has added additional cameras and increased nighttime security patrols.
It also said two missing emperor marmosets were likely to remain close to their habitat, but a search of the zoo grounds failed to locate them.
Animals have escaped enclosures at the Dallas Zoo before, and in 2004 Jabari, a 340-pound (154-kilogram) gorilla, leaped over a wall.
He went on a 40-minute rampage, injuring three people, before being shot dead by police.