The San Francisco Police Department reports that the beloved squirrel monkey named Banana Sam, who had been stolen days before from the San Francisco Zoo, had been rescued and was back in the zoo's custody Saturday evening.

The 17-year-old primate was believed to be taken late Thursday by thieves who appeared to have cut through a back perimeter gate and then made two holes into the mesh surrounding the monkey exhibit.

A reward, initially offered at $1,000 for Banana Sam's safe return, had been increased to $5,000 thanks to a pledge from a private donor, zoo spokesman Danny Latham said late Friday.

Security at the zoo was also increased; on Thursday night, two security guards were reportedly working when the Banana Sam was taken. Since then, security was doubled.

Minutes before 9 p.m. Saturday, police reported that Sam had been seen in a tree by a local resident walking through Stern Grove park. 

The good Samaritan successfully coaxed Banana Sam into his backpack, according to Sgt. Daryl Fong.

The man called police, and within an hour they met with zoo officials, who verified the monkey's identity.

As of 9 p.m., Sam had been returned to the zoo without injury, though he was described as being "hungry, trembling and thirsty," Latham said in a statement.

It was unclear whether or not the rescuer had recieved the $5,000 reward for his return.

"We are so thankful to the community and to the San Francisco Police Department for this happy ending," zoo director Tanya Peterson said in a statement. "I know it's been extremely stressful for zoo staff during this time but we are grateful Banana Sam is back at the zoo where he belongs."

As of Sunday morning, no one had been arrested for the monkey theft and no suspects had been identified.

"We're looking at every possible avenue, including the bystander," Manfredi said.

The zoo, which holds 17 squirrel monkeys other than Banana Sam, said it was concerned on many fronts after he was taken because he required a special diet to survive.. Also, while squirrel monkeys are not large animals, they have sharp teeth and will bite if provoked.

"This was a criminal act of vandalism and trespassing and we are working with the police to identify the perpetrators," said Tanya Peterson, president and executive director of the San Francisco Zoological Society Friday.

The zoo has had animal thefts before, according to the Associated Press: two teenagers were arrested 11 years ago on suspicion of stealing koalas to impress their girlfriends.

Common squirrel monkeys like Banana Sam are not endangered, and are often seen in pet markets and medical research. While some states allow keeping monkeys as pets, in California it is illegal.

News of the stolen monkey spread quickly on the Internet Friday, and someone set up a fake Twitter account tracking the alleged whereabouts of Banana Sam.