San Francisco Zoo officials are stepping up security after a male squirrel monkey was stolen from an exhibit.
Two security guards were patrolling the 100-acre zoo on Thursday night when the monkey named Banana Sam was apparently taken.
The San Francisco Chronicle reports that security has been doubled this holiday weekend in case the thieves try to return.
The zoo's remaining 17 squirrel monkeys are also now being kept indoors.
Banana Sam was taken after thieves cut through a back perimeter gate and then made two holes into the mesh surrounding the monkey exhibit. A $5,000 reward has been offered for the monkey's safe return.
The zoo has had animal thefts before. Two teenagers were arrested 11 years ago on suspicion of stealing koalas to impress their girlfriends.