Timeline: String of suspicious incidents under investigation at Dallas Zoo

Missing monkeys. Damaged enclosures. An "unusual" death.

The Dallas Zoo has been struck by a string of suspicious incidents in recent weeks that are under criminal investigation.

Here's a look at what's unfolded so far.

Jan. 13

A clouded leopard named Nova escaped from its enclosure after its fence was "intentionally cut," zoo officials said.

The zoo announced that morning it was closed due to a "code blue" -- meaning a non-dangerous animal was out of its habitat.

The Dallas Police Department was on-site assisting with the search efforts, and the leopard was eventually located around 4:40 p.m. local time on the zoo grounds near the original habitat.

Amid the search, police and zoo officials said they found a "suspicious opening" in the habitat wall at the front of the exhibit and determined the fence around the animal's enclosure had been "intentionally cut."

That same day, investigators discovered a second fence had been similarly cut at a habitat for langur monkeys, police said. No langurs escaped or appeared to be harmed, police said.

Police are investigating both incidents. It is unknown if they are related.

Jan. 21

Zoo officials discovered an endangered vulture dead inside its habitat. The death of the beloved animal -- a lappet-faced vulture named Pin -- was "unusual" and did not appear to be from natural causes, the zoo said.

A gross necropsy determined that the bird, which was at least 35 years old, suffered from a wound, said zoo officials. Dallas police were notified of the latest "suspicious" incident and are investigating, officials said.

Jan. 23

Dallas Zoo president and CEO Gregg Hudson announced the zoo is offering a $10,000 reward for information leading to an arrest and indictment "with these issues" during a press briefing on Pin's death.

Hudson also revealed that since the leopard's escape, the zoo has "substantially increased" its security camera coverage and more than doubled its security presence overnight.

Jan. 30

Two of the zoo's emperor tamarin monkeys were discovered missing from their habitat, which had been "intentionally compromised," the zoo said. Zoo officials alerted law enforcement officials about the missing monkeys.

"Based on the Dallas Police Department's initial assessment, they have reason to believe the tamarins were taken," the zoo said.

An "intentional cut" was made into the monkey enclosure, said Dallas police, which is investigating.

Jan. 31

Dallas police released a photo of an unidentified man they are looking to speak to about the missing tamarin monkeys.

The zoo announced several hours later that Dallas police had located the monkeys that evening. Dallas police received a tip that the monkeys may be at an abandoned home in Lancaster, a city in the Dallas area, and responding officers found the animals in a closet in the home shortly before 5 p.m. local time, police said.

No arrests have been made at this time and the investigation is ongoing, police said.

Feb. 1

The Dallas Zoo announced it is now offering a $25,000 reward -- up from $10,000 -- for information leading to the arrest of the person, or people, responsible for a string of incidents at the zoo.

Feb. 3

Dallas police arrested 24-year-old Davion Irvin -- a man they were looking to speak with earlier this week regarding the missing tamarin monkeys -- in connection with the theft of the two animals and charged him with six counts of animal cruelty.

The investigation into the case is still ongoing and further charges are possible, according to police.

Irvin was spotted near animal exhibits at the Dallas World Aquarium and flagged by someone who thought he looked like the person in the photo released by Dallas police Jan. 31.

ABC News' Nadine El-Bawab, Teddy Grant, Jon Haworth and Mark Osborne contributed to this report.