Remains believed to be of an American soldier killed in Cambodia decades ago during the Vietnam War were flown Monday to the U.S. for forensic analysis.

After a brief ceremony at Phnom Penh International Airport, a U.S. military transport plane left with the coffin holding the remains for a military laboratory in Hawaii, where tests to determine identification are to be conducted.

According to a statement from the U.S. Embassy, 55 Americans are still unaccounted for in Cambodia. More than 1,750 U.S. service members in all are still listed as missing in action from the Vietnam War.