North Korea has turned over what they say are an initial 55 casesholding remains believed to be of US troops killed during the Korean War.
After an initial assessment at an air base in South Korea, the remains will be flown to a US military laboratory in Hawaii for DNA analysis for what could be a lengthy and challenging process of identifying the remains and returning them to families.
So what could that process look like?
Their remains, military tags and uniforms will be examined
Scientists at the Defense POW/MIA Accounting Agency lab (DPAA) use forensic anthropology, forensic dentistry, DNA and other scientific methods.
The facility, named after the late Sen. Dan Inouye of Hawaii, describes itself as the largest forensic anthropology lab in the world. Scientists there analyze remains of missing service members from World War II, Korea and Vietnam, to match their DNAs and to return them to loved ones.
A genealogist who works on such cases looks at the soldiers' family tree and ancestries for possible DNA samples. During the process, forensic anthropologists also examine the human remains and material evidence, such as military uniforms, belongings and identification tags.
After that, the skeletal remains are examined to determine features such as sex, race, stature and age at death.
99% of troops don't have DNA on file
The next part includes DNA evidence and dental impressions to try to link them to missing military personnel.
One of the major issues is that the Korean War happened almost seven decades ago. About 99% of the service members from the Korean War and earlier conflicts don't have DNA on file, according to the Department of Defense.
"We have a genealogist who works cases just like that, where they go in and look at the family tree where their ancestries are so that we can possibly get a DNA sample that way," said said Army Sgt. 1st Class Shelia Cooper of the DPAA.
For years, the military has encouraged family members of Korean War soldiers to donate DNA that can be potentially used to identify their relatives' remains. But that can be challenging when some don't have biological family available to provide DNA samples.
Dental records are also critical, because if the person had a dental exam that contained X-rays, or any records and treatment, those can provide clues in the identification process.
Teeth and bones are crucial
Teeth and bones may also have some of the person's mitochondrial DNA, when all other soft tissue could have degraded.
The Hawaii lab uses mitochondrial DNA in about 75% of its cases, according to the DPAA. Those mitochondrial DNA sequences are compared to a family member who is maternally related to the unidentified American, as it's passed down only from the mother.
But there's a catch.
"Since these sequences are rare but not unique within the general population, they cannot stand alone as evidence for identification," according to DPAA.
All the reports go through a peer review process with external, independent experts, according to the agency.
Since the DNA technology started in the 1990s, the process of identifying remains has focused more on pulling mitochondrial and nuclear DNA from skeletal material.
The process of analyzing DNA is long and painstaking, and can sometimes take months or yearsdepending on what shape the remains are in.
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