A mystery is unfolding at the Dallas zoo as two emperor tamarin monkeys were reported missing on Monday in what is now the fourth recent incident involving animals at the popular attraction in Texas. Previously a vulture was apparently killed and a clouded leopard escaped after its cage was cut open. Before that another monkey cage was deliberately damaged. In the most recent twist of events, yet another enclosure appears to have been intentionally tampered with. Zoo officials confirmed a hole was found in the enclosure of the emperor tamarin monkeys and two are believed to have been stolen. In a statement, the zoo said: “Emperor tamarin monkeys would likely stay close to home – the zoo searched near their habitat and across zoo grounds, and did not locate them. Based on the Dallas police department’s initial assessment, they have reason to believe the tamarins were taken.” The series of events have stunned the institution. Last week, a 35-year-old endangered lappet-faced vulture named Pin suspiciously died with an unusual wound. Zoo officials mourned the bird’s demise and called the loss “devastating”. Earlier this month, the fencing of the clouded leopard enclosure appeared to have been intentionally cut open, allowing four-year-old Nova to escape before being safely returned home later that day. She was found on zoo grounds near her habitat. Before that, more primates were targeted. Another hole was found in the enclosure of the langur monkeys, but none got out. The latest crime happened despite the zoo increasing security and adding additional cameras on the premises. No arrests have been made so far and police have not confirmed whether the incidents are linked. A $10,000 reward is being offered for any information. According to the Smithsonian’s National Zoo and Conservation Biology Institute, emperor tamarins are native to the south-west Amazon basin. They are identifiable by their long white whiskers that resemble a moustache.