NEW YORK (NYTIMES) - For years, the rusty metal box lay entangled in poison ivy and trees in a Staten Island backyard. The homeowners thought it was just an electricity box.

But last month (April), they were amazed to discover that it was instead a locked safe that held money and jewels that they traced to a US$52,000 robbery in 2011.

And so began the tale of Bamboo Bob, the Ninja Burglar and the stolen treasure of Staten Island.

"It is like a childhood dream that you find treasure," said the homeowner, Mr Matthew Emanuel, who eventually tracked down the safe's owners. "I knew it was quite a find."

Mr Emanuel, a financial adviser for Bernard Herold & Co, and his family moved in to their house in the Todt Hill neighbourhood about four years ago.

From the deck and the couch in their family room, they could see the metal box on the edge of the property, but rarely paid attention to it.

"It was just a rusty box," he said. "Behind some trees."

In the spring, after winter storms and hungry deer ravaged their arborvitae trees and other vegetation, Mr Emanuel called in a horticulturist who specialises in exotic plants to help them plant bamboo on the side of the yard for more privacy.

On April 28, the man known as Bamboo Bob arrived. Bamboo Bob - whose real name is Robert Foley but who insisted on being referred to by his nickname in a telephone conversation - has been turning over the soil for decades as a landscaper in backyards, gardens and zoos in the New York and New Jersey areas.

When he paced around Mr Emanuel's backyard for the first time, he paused at the sight of the metal box, about 2 feet wide and 1.5 feet deep, embedded in a few inches of dirt.

"You never know what's under the ground," Mr Foley said. "Every job, I've got to know what's going on."

He asked Emanuel what the box was.

"He said, 'I don't know,'" Mr Foley said. "I said, 'How long have you lived here?'"

At closer inspection, Mr Foley and the other workers determined that it was not an electrical box after all. He helped the homeowners dig it from the dirt. They turned it over and saw a dial. It was a locked safe, disturbed from its hibernation 20 feet (6m) from Mr Emanuel's back door.

"I have seen it the whole time," Mr Emanuel said. "I have been throwing mulch on it."

The safe was heavy, about 80 to 100 pounds (36kg to 45kg). Mr Emanuel said he rocked it back and forth to see if he could hear jingling. They moved it to the deck, where it remained for the day as the landscapers worked.

Then they pried it open with a pick.

"The first thing we saw was stacks of hundreds, about three inches thick, wet and stuck together," Mr Foley said.

Inside were small bags of gold, diamond rings, earrings and other jewellery.

"It was mind-boggling," Mr Emanuel said. "There was so much gold I was using my kitchen scale. It probably weighed a pound or more."

Mr Emanuel said he did not call the police, but over the next few days, he said, he peeled apart some of the bills, drying them out and counting them. He said they added up to about US$16,000 in cash, mostly in US$100 denominations but some US$50 notes. Then he discovered an address on an item in the safe.

He searched online and linked the address to older neighbours whose house he passes while walking his dog. On April 30, Mr Emanuel knocked on their door.

"I have a strange question for you," he said. "Have you ever been robbed?" Mr Emanuel, who declined to provide the name of his neighbours, said the couple said yes.

They had been robbed during the days in 2011 when the so-called Ninja Burglar was roaming the neighbourhood.

"Well, I think I have your stuff," Mr Emanuel said he told them. "Why don't you come over to my house and I will show it to you?"

He and the wife walked around the corner.

He brought her into the kitchen and showed her the safe and its contents. "She was stunned."

The discovery revisited an unsettling time dating back more than a decade when the masked, prolific thief who became known as the Ninja Burglar preyed upon Todt Hill and other neighbourhoods.

Robert Costanzo, a convicted rapist, was eventually arrested in 2016 and admitted to investigators that he was responsible for more than 100 burglaries in which he stole more than US$4 million worth of property, the authorities said. "We got our guy," they announced at the time.

Officials said Costanzo had been active for a 10-year period until 2015. But the statute of limitations had expired in many of the cases and he was charged with just three counts of burglary. He was convicted and sentenced to 22 years in prison.

Still, the long-lost safe could have been his work. Residents at the address found by Mr Emanuel had reported in 2011 that their safe had been stolen with about US$40,000 in cash and jewellery, all worth up to US$52,000, a Police Department spokesman said.

"That was investigated as part of that Ninja burglary pattern," Mr Ryan Lavis, a spokesman for the Staten Island district attorney, said last Friday.

Mr Emanuel said that reporters all over the world had called him since the discovery was first reported by The Staten Island Advance and then picked up by television networks. One recurring question was why he returned the money and jewels.

He said: "I knew whose it was. When I did not know on Saturday night, I had all intentions of keeping it. But once Sunday came and I found out whose it was, I knew it was somebody else's.

"I couldn't walk past their house and live with myself knowing I had their stuff."