NEW YORK, NY..- During the brutal Battle of Okinawa in Japan, in the final months of World War II, a group of U.S. soldiers took residence in the palace of a royal family who had fled the fighting. When a palace steward returned after the war was over, he said later, the treasure was gone.

Some of those valuables surfaced decades later in the attic of the Massachusetts home of a World War II veteran, whom the FBI did not identify in announcing the find last week.

The veteran’s family discovered the cache of vibrant paintings and pottery; large fragile scrolls; and an intricate hand-drawn map after his death last year, and they reported the discovery to the agency’s Art Crime Team.

Geoffrey Kelly, a special agent and the art theft coordinator for the bureau’s Boston field office, was assigned to the case and brought the artifacts to the National Museum of Asian Art at the Smithsonian Institution in Washington. The recovered items were returned to Okinawa in January, and a formal repatriation ceremony is planned to take place next month in Japan.

“It’s an exciting moment when you watch the scrolls unfurl in front of you, and you just witness history, and you witness something that hasn’t been seen by many people in a very long time,” he said.

Verified by Smithsonian experts as authentic artifacts of the erstwhile Ryukyu Kingdom, a 450-year-old dynasty that ruled in Okinawa as a tributary state of the Ming dynasty of China, the items were turned over by the FBI to the U.S. Army Civil Affairs and Psychological Operations Command. Its cultural heritage specialists returned the precious pieces to Okinawa.

“Very few items survived from that kingdom,” said Travis Seifman, an associate professor with the Art Research Center at Ritsumeikan University in Kyoto, Japan. “Recouping heritage, recouping cultural treasures, knowledge of their own history is a really big deal for a lot of people in Okinawa.”

The Ryukyu Kingdom ruled in Okinawa from the early 15th century until 1879, when Japan annexed the kingdom as a prefecture.

The cache of 22 artifacts from the 18th and 19th centuries includes two portraits of Ryukyu kings — the only two of as many as 100 painted that are known to have survived the war — “an incredible find,” he said.

A typewritten letter, written by a U.S. soldier who was stationed in the Pacific theater during World War II, was found with the artifacts and indicated that the items had been taken from Okinawa, authorities said.

The letter described smuggling the pieces out of Japan and trying — and failing — to sell them to a museum in the United States, said Col. Andrew Scott DeJesse, the cultural heritage preservation officer who accompanied the artifacts back to Okinawa.

The veteran, who was posted in Europe, found the artifacts near a dumpster, DeJesse said, and recognizing their value, took them home to Massachusetts.

“Samurai swords, katanas, things on military personnel, that was always accepted,” DeJesse said, describing how American commanders approved service members’ war trophies from the battlefield.

During World War II, cultural heritage investigators known as Monuments officers were in Europe tracking down millions of artworks, books and other valuables stolen by the Nazis. Officers were also stationed in Japan, “but the looting of heritage sites,” DeJesse said, was “not really known.” Americans, he added, weren’t the only ones who took items from war zones.

“The Japanese Empire was doing it all over the place. So were the Nazis, so was the Soviet Union. It was done systematically,” he said.

The Battle of Okinawa, which has been described as “82 days of the costliest fighting in the Pacific,” was among the bloodiest campaigns of World War II. About 100,000 Japanese civilians and 60,000 troops were killed. More than 12,000 soldiers, sailors and Marines died in the three-month battle. Artwork and other valuables were not the only items stolen. Some researchers have said that U.S. soldiers took skulls and other body parts as trophies.

After the war ended in 1945, Bokei Maehira, a palace steward, returned to the palace to check on the heirlooms — which included crowns, silk robes, royal portraits and other artifacts — that he and others had hidden in a trench on the palace grounds. He found the palace reduced to ashes, and the trench plundered, he wrote in an academic paper published in 2018.

Among the loot was “Omorosaushi,” a collection of Ryukyuan folk songs that dated back centuries.

The U.S. government repatriated the Omorosaushi to Okinawa in 1953, after a U.S. commander, Carl W. Sternfelt, brought the war booty to Harvard University for appraisal.

In 1954, the United States joined dozens of other countries in signing the Hague Convention, a treaty brokered by the United Nations to protect cultural property in armed conflict.

Still, DeJesse, who served two tours in Afghanistan and one in Iraq, said that part of his and other heritage officers’ work is training military commanders and soldiers who are unaware of that obligation.

“It’s a major problem. We advise them, ‘Hey, don’t touch it, don’t pick it up. It’s someone else’s. Just like you wouldn’t want your own church, your own museum looted,’” he said.

The government of Japan registered other missing Ryukyu Kingdom articles with the FBI’s National Stolen Art File in 2001. They include black-and-white photos depicting a collection of significant Okinawan cultural patrimony that, according to Seifman, “are in many cases all that survive of sites and objects lost or destroyed” in World War II.

Among the items registered were the scrolls found in the Massachusetts veteran’s attic.

The veteran’s family, to whom the FBI has granted anonymity, will not face prosecution.

“It’s not always about prosecutions and putting someone in jail,” Kelly said. “A lot of what we do is making sure stolen property gets back to its rightful owners even if it’s many generations down the road.”

This article originally appeared in The New York Times.