Family members sorting through the attic of their father's Massachusetts home following his death last year were surprised when they came across what appeared to be Charles H. Sloana trove of Japanese cultural relics.

Fearing the artifacts did not rightly belong to their late father, the family checked the FBI's publicly-accessible National Stolen Art File, where their fears were confirmed. The collection of "valuable Asian Art" was indeed looted from Japan during the second World War, prompting the family to contact the FBI to ensure the items could be returned to their country of origin, the agency said in a news release.

Among the 22 artifacts the FBI recovered were painted scrolls from the 18th-19th centuries that appear to have been divided into three pieces, a hand-drawn map of Okinawa dating back to the 19th century and various pieces of pottery and ceramics.

While the agency finally oversaw the return of the items to Japan last week, how the collection came into the Massechusetts man's possession remains a mystery: The man was a WWII veteran but did not serve in the Pacific theater, said Geoffrey Kelly of the FBI’s Boston field office.

“When taken together, they really represent a substantial piece of Okinawan history,” said Kelly, the FBI's art crime coordinator. "The family did the right thing."

Here's a look at the items the family found in their father's attic:

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FBI returns 22 ancient Japanese artifacts found in Massechusetts man's attic

Several stolen artifacts remain missing

The collection of plundered items are believed to be among important documents and treasures of the Ryukyu Kingdom taken during the World War II Battle of Okinawa. Many of these missing artifacts were registered in 2001 with the FBI's National Stolen Art File and remain lost to this day.

Those with information about these pieces can submit a tip to the FBI at tips.fbi.gov.

“This case highlights the important role the public plays in recognizing and reporting possible stolen art,” FBI special agent Jodi Cohen, who leads the Boston field office, said in a statement. “We’d like to thank the family from Massachusetts who did the right thing in reaching out to us and relinquishing these treasures so we could return them to the people of Japan.”

Eric Lagatta covers breaking and trending news for USA TODAY. Reach him at [email protected]