As private wealth grows, protecting the world's cultural assets, including those from South-east Asia, grows more challenging.
With their long and rich history, large parts of Asia know this tragedy all too well as colonisers and collectors have plundered ancient capitals and temples. Examples abound of Khmer sculptures from Cambodia and Buddhist images from Myanmar and Thailand of uncertain provenance crossing international borders and making their way into private collections and museum galleries, and onto auction blocks.
This continues despite there being both international agreements and national laws intended to protect the region's heritage.
In the 1960s and early 1970s, with thefts increasing both at museums and archaeological sites, a United Nations Educational, Scientific and Cultural Organisation (Unesco) convention was developed to prohibit the illegal import, export and transfer of cultural property.
That convention and a subsequent one, however, failed to win universal support. Due, in part, to concerns about definitions of what is a "cultural property", compensation, enforcement and national sovereignty, the initial 1970 Convention has been ratified to date by only 131 out of 195 member states of Unesco.
Of the 10 Asean nations, only Cambodia, Laos, Myanmar and Vietnam have ratified or accepted the convention, according to the Unesco website.
For the most part, existing measures to protect Asia's rich heritage have proven inadequate.
According to The Diplomat magazine, the worldwide illicit trade in antiquities and other works of art is worth US$6 billion (S$8.2 billion) a year based on data from Global Financial Integrity, a non-profit advocacy organisation in Washington.
RIGHTING PAST WRONGS
However, there has been some progress in South-east Asia in righting past wrongs.
In 2013, a unique 11th-century statue of Buddha from the world-famous Bagan temple complex was returned to Myanmar, thanks in large part to the work of individuals associated with Northern Illinois University (NIU), including Dr Richard Cooler, its professor emeritus of art history and founder and former director of the Centre for Burma Studies.
Around half a metre in height, the rare statue of a standing Buddha had been stolen from Bagan in 1989 by an unknown individual, according to NIU, after which, it appeared in Bangkok, was sold to an art dealer in San Francisco, and then listed for sale by Sotheby's auction house, before the United States Federal Bureau of Investigation ultimately got involved.
In another example, in 2014, the US returned to Thailand hundreds of artefacts, including ancient bronze tools and pottery, stolen from an archaeological site in north-east Thailand.
The Ban Chiang artefacts had been found in a 2008 raid of the Bowers Museum in California following a five-year investigation into an antiquities smuggling ring and tax fraud involving a California art dealer.
Last October, Norwegian art collector and businessman Morten Bosterud returned the head of a ninth-century "head of Shiva" statue along with a 12th-century "head of a male divinity" statue to Cambodia.
Mr Bosterud did not elaborate at the handover ceremony on how he came into possession of the artefacts, simply saying that he had come to realise that "they belong to the Cambodian people".
And in March, the Denver Art Museum voluntarily returned to Cambodia a 10th-century statue of the Hindu deity Rama that had been stolen from the Prasat Chen temple at the Koh Ker complex, not far from Angkor Wat.
The museum had acquired the piece in 1986, unaware that the massive sandstone statue's provenance was in question.
Sadly, no one really knows how many plundered cultural artefacts from South-east Asia are in private hands around the world.
THREE WAYS FORWARD
However, there is a path forward, and policymakers, museum directors, would-be collectors and other stakeholders can lead the way.
First, education is critical. Greater emphasis should be placed on educating all stakeholders about Asia's heritage, and the importance and means by which to conserve and protect it.
Changing attitudes towards what is appropriate to collect will take time and education. With the Asean Socio-Cultural Community being one of the three pillars of the Asean Community, a framework already exists for nurturing the region's shared identity, culture and heritage.
The region's museums, private galleries and art dealers must also step up, given their important role on the frontlines of the international art market.
Second, enforcement of existing laws must be strengthened. There can be no more "blind eyes" when it comes to illicit trade, whether of art or persons. While few of Asean's member states have signed the 1970 Unesco convention, national laws have been adopted to reduce illicit trade, including of protected cultural assets. Thailand has had, for decades, an antiquity law, passed in 1961, forbidding certain exports.
While funding for the enforcement of relevant laws in the poorest of Asean's nations may well remain limited, there is a need and opportunity for greater cooperation and support across the region.
Change will require greater intelligence-sharing among all appropriate agencies at an international level to prevent illicit items entering the open market. This has taken on more importance in the last few years as so-called "blood antiquities" - artefacts looted from conflict zones and sold to finance terrorism - have been documented.
Third, enhanced technology can be deployed to tackle the problem. New advances, including the development of apps and other technology tools to better document and track an item's provenance, need to be piloted, tested and applied.
The Antiquities Coalition, a Washington-based non-profit organisation, is one example of a cross-sector partnership using its resources, relationships and the power of technology and communications to "fight against cultural racketeering" and "safeguard our shared cultural heritage".
A nation's cultural artefacts are windows to its history and can serve as inspiration for future generations. Cambodia, with the richness of its Khmer heritage including the temples of Angkor, is one shining example of South-east Asia's cultural diversity and heritage. As that nation moves forward from its tragic past, its citizens deserve their treasures to be protected and, as appropriate, returned home.
"I came to realise that the (pair of Khmer artefacts I had) are not to be held by a person like myself," said Mr Bosterud. "These beautiful artefacts belong to the true owners, the Cambodian people," The Cambodia Daily reported Mr Bosterud as having said in his speech at the recent repatriation ceremony at the National Museum in Phnom Penh.
We couldn't agree more.
- Curtis S. Chin, a former US ambassador to the Asian Development Bank, is managing director of advisory firm RiverPeak Group. Jose B. Collazo, a South-east Asian analyst, is an associate with the group.