The Pacific Beat reported that a total of 42,000 individual items from all over the world — including human remains — were found in the home of a private collector five years ago.
The home belonged to a 91-year-old man called Don Miller, who has since died.
He had been a Christian missionary and had collected some the items from around the world over his lifetime.
"We seized those artefacts that we felt were problematic, that were outright illegal or had been obtained improperly," Special Agent Tim Carpenter from the FBI's special Arts Theft team.
They include Ming vases, Native American arrowheads and the human remains of around 500 people.
There are around 100 artefacts from PNG.
The FBI wants to return those to their rightful countries of origin and owners, but tracking down the relevant people is proving difficult, including in PNG.
Since the items were seized five years ago, they have managed to repatriate just 15 percent, which has prompted the FBI to recently go public with an appeal for help.
"We've not had as good a response as we'd hoped, and this is one of the reasons we'd gone public. Our hope is can generate renewed interest in this case and encourage these countries to come forward and claim their materials," Agent Carpenter told Pacific Beat.
Pacific Beat sent photos of some of the PNG items to a senior curator from the Macleay Museum in Sydney, Dr Jude Philp, who works with PNG artefacts.
“The items are all typical of collections from PNG of the 19th century. Although similar kinds of things are still made today for local and foreign audiences, the way that these have been made indicates most are of an older tradition," Dr Philp responded.
"It is now very difficult to know where these will have come from. Lots of people collect PNG things...some people do collect assuming that they will take better care and have better knowledge of things and at times this impulse seems to lurch over to a kind of mania and has the potential to extend to theft and illegal purchase.”
The FBI's Tim Carpenter is undeterred by the size of the task at hand, and he is adamant they will keep trying to return the items.
"I'd like to think that we get closure and justice in this case by seeing it through, and returning these ancestors and objects they were buried with back to their rightful place of ownership. That's the small part the FBI can do to right this wrong," he said.