The reward for Banana Sam has been put on hold while police investigate the story of the person who found the monkey.

It seems as if there could be some monkey business involved  in the return of kidnapped primate Banana Sam, and the $5,000 reward has been put on hold while police investigate.

"It's not anything out of the ordinary. We're not ruling anything out," Carlos Manfredi, a spokesman for the San Francisco Police Department, told ABC News.  "Investigators want to make sure they cover all the bases."

A man said he found the black-and-orange monkey, who is 17 years old, last Saturday,  two days after  Banana Sam  disappeared from the San Francisco Zoo.  The man told police he'd been out walking his dog when he spotted  the 2-pound monkey and coaxed it  from a bush and into his backpack.

But primate experts don't buy the story.

Jill Andrews, the zoo's assistant curator of primates, told the San Francisco Chronicle that squirrel monkeys aren't likely to  hop willingly  into a backpack.

Banana Sam disappeared from his home at the zoo  late last Thursday night or early Friday morning, when  zoo employees  reported him missing from his enclosure.  Zoo officials quickly found signs of a break-in: two holes cut in the wire mesh cage and the chain on the perimeter fence cut.

"The one hole is fairly small and it's right by where their nest box is that they sleep in at night. The other hole on the other panel is fairly large,  a small person could certainly go in," Corinne Macdonald, the curator of primates at the San Francisco Zoo, told ABC News.

The identity of the man who found Banana Sam has not been released.

ABC News' Olivia Katrandjian contributed to this story.