City police said the 17-year-old squirrel monkey was spotted in a bush in Stern Grove Park by a visitor who coaxed him into a backpack, the San Francisco Chronicle reported. Police brought Banana-Sam back to the zoo at 7:45 p.m..
The newspaper said he was checked out by staff and found to be "hungry, trembling and thirsty," although in good physical condition overall.
"We are so thankful to the community and to the San Francisco Police Department for this happy ending," said Tanya Peterson, the zoo's executive director. "I know it's been extremely stressful for zoo staff during this time but we are grateful that Banana-Sam is back at the Zoo where he belongs."
Zoo officials said the monkey was snatched from his cage either late Thursday or early Friday.
"This was a criminal act of vandalism and trespassing, and we are working with the police to identify the perpetrators," Peterson said prior to Banana-Sam's return.
Squirrel monkeys, which can weigh up to 3 pounds, do not make good pets, Peterson said.
"He has extremely sharp teeth and will definitely bite if provoked," zoo officials said in an earlier statement.