The University of California, Davis, Police Department has determined after an investigation that a healthy rhesus macaque monkey missing from the campus's California National Primate Research Center most likely became trapped in the center's drainage system and has probably perished.

Center employees, including those who had last seen the 2-year-old female monkey, voluntarily cooperated in the investigation. The Yolo County District Attorney's Office assisted in employing a computer voice stress analyzer. The truth verification system verified the employees' account, according to UC Davis Police Chief Calvin Handy.

"We are confident in this case that an unfortunate accident occurred that likely has resulted in the death of this animal," Handy said. "We are recommending a complete flushing of the utility system in the hope that her remains can be recovered."

The monkey was reported missing Feb. 13 by two animal handlers who said the animal darted out of its indoor cage during routine cleaning, then went behind a row of cages and that noises were heard from the room's drain hole.

"It's very disappointing and for many of us heartbreaking that we have lost an animal in this fashion," said primate center director Dallas Hyde. "As a result of this incident we are reviewing security and safety policies and procedures and will be further heightening our internal security at the primate center with increased surveillance."

Hyde said the center is conducting an administrative review of the employees' handling of the animal. "Last fall we completed 10 weeks of training and we will do more training and provide more direct supervision of our staff."

The Office of the Vice Chancellor of Research has also appointed an oversight committee to examine primate center safety and security. It has begun meeting and includes representatives from the campus offices of environmental health and safety, research, police and the primate center.

Security at the primate center was already in the process of being heightened in compliance with new guidelines set out in the federal Patriot Act. Many of those measures will take effect in phases this spring. The campus is also exploring the legality of conducting video surveillance and requiring background checks on all 276 primate center employees.

The primate center houses 4,279 monkeys in a combination of indoor and outdoor facilities. Every year three or four monkeys manage to get out of their outdoor enclosures and are quickly recovered without leaving the premises. This is the first time in the 40-year-operation of the primate center that a monkey has remained unaccounted for.

The juvenile tan and gray monkey stood about 20 inches high, weighed 4.4 pounds and was small enough to fit through the four-inch opening that led to an eight-inch and wider piping system. The monkey was part of the center's disease-free group of animals, and was intended to become part of the breeding colony.

In the course of the police investigation, employees were interviewed, the 300-acre primate center grounds were again searched and sections of the sewer system again explored. This drainage and sewer system contains hundreds of yards of piping, as well as grinders and screens. The waste then goes to the campus wastewater treatment plant.

Located on County Road 98, at the end of Hutchison Drive, the primate facility is one of eight regional primate centers supported by the National Institutes of Health to conduct research in selected areas related to human health. To support its research program, the center maintains a large primate-breeding program.

The center also provides monkeys, mostly rhesus macaques, to research programs at seven UC campuses and other research institutions nationwide. These programs include studies of cancer, asthma, AIDS, osteoporosis, neurodegenerative diseases, and infant development and nutrition.