The series of suspicious events could not stop at the Dallas Zoo in the American state of Texas.
After the escape of a leopard and the mysterious death of a rare vulture in the past few days, two emperors disappeared mysteriously on Monday.
The police were alerted on Monday after keepers found two emperor monkeys missing from the zoo and have not yet been found.
Police say they are investigating the disappearance of the monkeys, but no arrests have been made at this time. Dallas police have declined to say whether the incidents are related.
The police have suspected that someone has taken the two monkeys.
The emperor monkey is famous for its long white moustache. They are believed to have been named after William II, the last emperor of Germany, who had a long moustache.
A series of suspicious incidents at the Dallas Zoo began earlier this month when a cheetah escaped from its cage and was later found safe.
Last week, an extremely rare vulture was found dead with “unusual injuries” at the zoo. The vulture was one of only 6,000 on the planet and its death is being treated as “suspicious”, with zoo staff saying it is devastating to lose the vulture, who will be “deeply missed by everyone”.
Ed Henson, chief executive of the American Association of Zookeepers, said it appears someone “really has a problem with the Dallas Zoo.” Since the unusual incidents began, the zoo has added additional cameras and Security patrols have also been increased at night.
The zoo is spread over 106 acres with over 2,000 animals and is the oldest and largest zoo in Texas. It hit the headlines in 2004 when a guerrilla escaped and injured 4 people, who was later shot dead.