A pair of emperor tamarin monkeys disappeared from their enclosure at the Dallas Zoo and are believed to have been taken, the latest suspicious incident involving an animal or a habitat at the zoo, authorities said Monday.

In a statement, the zoo said it alerted the Dallas Police Department to the missing animals Monday morning after facility staff found their habitat had been “intentionally compromised.”

The animals would likely stay close to their enclosure, the zoo said, and employees could not find them during a search of facility grounds.

A police department spokeswoman said a preliminary investigation revealed an intentional cut to the habitat. Investigators believe the animals were taken, the department said.

The zoo declined to comment further and the police department said its investigation was continuing.

The disappearance comes after three other incidents, including the death of Pin, an endangered vulture who was found on Jan. 21 with what zoo officials described as an “unusual wound.”

A cause of death wasn’t clear. A zoo spokeswoman said Monday that officials were still awaiting the final lab results of a necropsy.

On Jan. 13, Nova, a 3-year-old clouded leopard, fled from her wire mesh enclosure after an incision was made in it, authorities said. The zoo closed for the day and the animal — which the zoo said posed no danger to the public — was found later that day.

As authorities were investigating Nova’s escape, they found a similar cut at the habitat that houses langur monkeys. None of the animals escaped or were harmed or taken, the Dallas Police Department said at the time.

It isn’t clear if the incidents are linked, but the zoo said it was stepping up security measures, adding more overnight guards and cameras. It also offered a $10,000 reward for information leading to an arrest and an indictment.