A historical mystery about the final resting places of George Washington’s younger brother, Samuel, and Samuel’s family has been partially solved thanks to a DNA study.

The research, published in the journal iScience, identified the first president’s grandnephews—George Steptoe Washington Jr. and Dr. Samuel Walter Washington—and their mother, Lucinda “Lucy” Payne—based on skeletal remains found in unmarked graves at a cemetery in Samuel Washington’s Harewood estate near Charles Town in West Virginia.

Researchers looking for Samuel’s final resting place had excavated five unmarked graves at the estate in 1999. The dig found small bones and teeth that had badly degraded over the decades, and DNA testing at the time gave inconclusive results.

The new study employed multiple types of analysis, including testing of Y-DNA, mitochondrial DNA, and autosomal DNA to establish a more definitive picture. It also compared the genetic data recovered from the bones with the DNA of a living descendant of Samuel Washington.

The results showed that the living descendant is the great-great-grandson of Dr. Samuel Walter Washington, and they also allowed the researchers to establish which of the remains belonged to which of President Washington’s grandnephews.

It is hoped that the techniques used in the study could be used to help identify the unidentified remains of people who served in the military dating back as far as World War II, the study says. The findings, which led to the first Y-chromosomal DNA profile of George Washington, also could be used to help people with the Washington name but who are unsure of their family history to “determine who is paternally related to George Washington himself.”

Senior study author Charla Marshall, a molecular anthropologist and deputy director of the Department of Defense DNA Operations, said the final resting place of the Founding Father’s brother was not identified. “The search for Samuel Washington’s grave is no longer underway,” Marshall told CNN. “It is possible that his grave was exhumed long ago, and may never be found again.”