An endangered vulture was found dead in its enclosure at a Texas zoo with "an unusual wound", officials said on Monday.
The bird's death occurred just over a week after the mysterious disappearance of a clouded leopard that escaped from its exhibit through a cut-out hole.
Police have been asked to look into the death of the rare lappet-faced bird - one of 6,500 on the planet.
Results from a necropsy report deemed the death "very suspicious".
"The death does not appear to be from natural causes," zoo officials said in a statement. No further details where given due to the ongoing investigation.
"If it's related to anything that happened to the clouded leopard before, it goes from being about malicious and gets really into criminal intent," the zoo's president Greg Hudson said at a press conference. "That is dangerous, and we're extremely concerned about it."
It was the third suspicious incident at the zoo in less than two weeks.
A three-year-old clouded leopard escaped from her enclosure on 13 January, prompting a "code blue" alert indicating that a non-dangerous animal was on the loose.
Zoo staff members also found deliberate cuts on the enclosure that houses langur monkeys.
A spokesperson for the Dallas Police Department said the US Fish and Wildlife Service had been called to assist with the investigation into the vulture's death.
The zoo has recently ramped up its security efforts across the 110-acre campus, Mr Hudson said, including doubling the number of overnight security guards and adding to the 100-plus cameras already on zoo grounds. It is also offering a $10,000 (£8,122) reward for information leading to an arrest and indictment, according to a statement from the zoo.
The lappet-faced vulture, named Pin, was 35 years old and had been at the Dallas Zoo for 32 years, during which time he sired 11 offspring and one grandchild.
"A lot of people knew him very well having worked with him for so long," said Harrison Edell, vice president for animal care and conservation at the Dallas Zoo.
The bird was one of only 27 lappet-faced vultures in US zoos, and the species could move to critically endangered in our lifetime, he added. There only about 6,500 of the birds left globally, 41 in zoos outside of the US.
"We're really disturbed by the idea that someone might have intentionally done this," Mr Edell said.