Personnel from DPAA and Republic of Korea Army (ROKA) Soldiers conduct excavation operations in Yanggu, South Korea, May 8, 2017. Eight members of DPAA deployed to South Korea to attempt to recover the remains of a missing service member lost during the Korean War. (Photo: U.S. Army/Staff Sgt. Roy C. Woo)

About 5,300 American soldiers remain in the soil of North Korea, casualties in a war that has never officially ended.

The new talks between U.S. President Donald Trump and Kim Jong Un of North Korea lasted several hours yesterday in Singapore. The lofty principles outlined by the end were complete denuclearization of the peninsula, and a cessation of U.S.-South Korean military exercises.

Also among the promised goals: collecting all the American casualties from the 1950-1953 conflict—and bringing them home.

Returning the remains may be as daunting as the other strategic goals, if history is judge.

The final part of the Trump-Kim joint statement states, “The United States and the DPRK [Democratic People's Republic of Korea] commit to recovering POW/MIA remains, including the immediate repatriation of those already identified.”

The U.S. agency responsible for bringing the dead home, the Defense POW-MIA Accounting Agency (DPAA) already knows where almost all the remains are to be found—but they have not had access to the most isolated country on Earth for more than a decade.

A series of locations in the DPRK are thought to house the vast majority of the missing and presumed dead.

More than a half-dozen POW camps each old hundreds apiece; the Apex Camps, Camp 5 on the south bank of the Yalu River, the main Death Valley Camp also known as Pukchin-Tarigol, the Valley #1 complex, and the villages of the Suan Camps all have remains that, together, could answer many mysteries. Most of these American dead died during the especially harsh and brutal winter of 1950-1951.

Battle zones, including the Chosin Reservoir and the combined Unsan and Chongon River areas of conflict, could boast thousands more. Those two alone could have approximately 2,800, according to the DPAA.

Another 1,000 could be recovered from the Demilitarized Zone between the two Koreas, the agency adds.

Military cemeteries left behind in the DPRK by retreating U.S. and U.N forces could remain, despite previous Communist efforts to gather the remains in previous exchanges.

Some 600 DPAA workers, including anthropologists and dental experts, could have much work ahead of them, if the deal results in forensic teams on the ground in the DPRK.

Virtually all of the work will be DNA work from bones, depending on the conditions of the 60-year-old remains. But recent forensic breakthroughs in sequencing smaller and smaller biological samples from the bones of the inner-ear and from the center of the long bones have meant more and more identification from 20th century war casualties than ever before. Just this week, two more Korean War soldiers were accounted for—along with three veterans from World War II (two of whom were from the U.S.S. Oklahoma). 

One of the major breakthroughs has been with next-generation sequencing, also known as massively parallel sequencing. For instance, in one recently-reported case, a humerus bone from the Korean War yielded only seven loci to conventional STR typing—but next-gen produced 21 markers, along with distinct Y-STRs and SNPs to produce a fully-convincing identification.

Historically, there have been efforts to repatriate the remains. Operation Glory, an armistice-required effort between the U.S. and North Korea and their Chinese allies, returned 4,167 containers in late 1954. But efforts have been intermittent ever since. Unilateral turnovers were made by the DPRK between 1990 and 1994, and also in 2007.

The DPAA conducted its own fieldwork in the DPRK from 1996 through 2005—but the agency ceased operations when it stated it could no longer guarantee the safety of its workers in the country. Critics also said that the North Koreans were attempting to profit from the venture, which yielded 229 sets of human remains at a cost of $20 million.

Talks over re-starting the work ceased in 2011, after North Korea resumed some ballistic weapons testing.

The overall death estimate for the Korean War, like all conflicts, varies. But historians think about 1.5 million Chinese and North Koreans perished from 1950 to 1953, while on the other side 400,000 South Koreans, 30,000 U.S. and 1,000 other service members are listed as casualties. The armistice signed in 1953 was never followed by a formal peace treaty.