Investigators have charged Douglas A. J. Latchford, a leading expert on Khmer antiquities, with smuggling looted Cambodian relics and helping to sell them on the international art market by concealing their tainted histories with falsified documentation.

In a federal indictment unsealed on Wednesday, Mr. Latchford, 88, was accused of having served for decades as a “conduit” for Cambodian antiquities that had been excavated illegally from ancient jungle temples during unrest in the country starting in the mid-1960s, with the beginnings of the Cambodian civil war.

According to a news release from the United States Attorney’s Office for the Southern District of New York, Mr. Latchford, a dual citizen of Thailand and the United Kingdom, falsified invoices and shipping documents to make it easier to sell those looted artifacts to major auction houses, dealers and museums.

The prosecutors presented in its court papers a sordid and alternative perspective on Mr. Latchford, who had been hailed in Cambodia as a protector of the country’s relics, having donated rare artifacts and money to the national museum in Phnom Penh. In 2008, he was honored with the country’s equivalent of a knighthood. He is also the co-author of three books — “Adoration and Glory: The Golden Age of Khmer Art,” “Khmer Gold” and “Khmer Bronzes” — that are foundational reference works for experts.