Cynomolgus monkeys can cost up to $10,000 each and have been in demand for coronavirus vaccine research, according to the New York Times.
The crash in Pennsylvania of a truck transporting 100 monkeys to a laboratory has allowed four of them to escape, triggering a search by police who warned the public not to approach the animals.
The vehicle collided with a dump truck near Danville, Pennsylvania on Friday afternoon, en route to a laboratory in Florida.
Police said on Twitter that four monkeys had "fled the crash scene into the surrounding area."
Three were later captured, but one was still on the loose on Saturday morning.
The local WNEP news site said a police helicopter with thermal cameras was used to track down the cynomolgus monkeys, while officers on the ground used powerful flashlights.
Pennsylvania State Police released an image of one primate perched in a tree off Route 54 during the freezing cold night.
A reporter said police surrounded the monkey before shots were fired from an unidentified weapon.
"Crash Update: There is still one monkey unaccounted for, but we are asking that no one attempt to look for or capture the animal," police troopers said on Twitter on Saturday morning.
Cynomolgus monkeys -- also known as long-tailed macaques -- can cost up to $10,000 each and have been in demand for coronavirus vaccine research, according to the New York Times. They can live for 30 years in captivity.