The discovery of at least two unmarked and unrecorded veterans graves at the Vicksburg National Military Park cemetery has archaeologists and park officials trying to solve a mystery.

“Each time we think we found an answer, three or four more questions pop up,” said VNMP Superintendent Michael Madell. “We are hoping the golden nugget is out there.”

The burial ground, located on a 1.9-acre tract parallel to North Washington Street, was used from the 1940s until 1961 to bury veterans of World War II and Korea. In 1961, the park, with 18,000 buried soldiers from wars spanning the last 150 years, stopped accepting burials, unless reservations had been made before.

In August, Louis Spencer Jr., a Vicksburg native and founding member of the popular singing group Red Tops, died in Vicksburg. Upon excavating land for his reserved spot, a small corner of a wooden casket with metal edges appeared. Digging in a plot next to the original also revealed part of a casket.

Spencer’s body was placed in a separate part of the cemetery as work began to solve the mystery of how two unmarked and unrecorded graves made it to the western edge of the park.

“We have found nothing to show who may be buried there or why the graves were not marked,” Madell said.

On Jan. 3, members of the Southeast Archaeological Center in Tallahassee, Fla., part of the National Park Service, began surveying the cemetery grounds using Ground Penetrating Radar to detect anomalies.

The system used probes and an antenna to transmit thousands of radar pulses into the ground. The pulses change speed when encountering different sediment or objects below. After collecting radar images — changes of color and frequency but not actually visual evidence — the maps were overlayed with actual marked gravesites, exposing several shapes and colors the team believes are the unmarked graves.

Within that half acre, eight to 10 likely unmarked graves were found and possibly 48 others whose status will require further research.

This week, SEAC members were back at the park using both GPR and electrical sensitivity meters to probe the possible sites. When that data is recorded, it will be combined with known gravesites and the GPR data to further decipher if and where the burial plots are located.

“We move at 50 centimeters at a time and zigzag across the cemetery,” SEAC member Drew Wise said. “It’s very slow but we have gotten good results so far.”

David Morgan, SEAC director, said the layout of this part of the cemetery with its systematic placing of headstones makes this project more unusual than others. Walking through the cemetery, headstones are lined in a pattern, but scattered throughout are empty areas that appear to be the right size and distance for burial plots.

“What’s unusual are the vacancies in the systematic pattern of the burial sites,” Morgan said.

Several small burial markers — small, round metal plates — were unearthed about 5 inches below the earth, but no markings or indications of when or who placed them has been found. Park records so far have turned up no reason for the unmarked graves.

While SEAC continues to do physical research, park officials are combing records in Vicksburg and at other national parks, as well as at funeral homes and city and county data.

The likelihood of discovering the identities of those buried is minimal, due to concerns ranging from cost to not wanting to disturb the gravesites. Madell said when SEAC research is completed and the graves are properly plotted, the park will have a memorial service to honor those buried.

“The National Park Service takes the stewardship of this final resting place very seriously,” Madell said. “We apologize to these individuals and their families.”

Park historian Terry Winschel said more than 18,000 veterans are buried in the cemetery, most of those having died in and around the 1863 Siege of Vicksburg. Of the 17,000 Union dead, about 13,000 of those are unidentified. Confederate soldiers, with the exception of one, are buried at Soldier’s Rest in Cedar Hill Cemetery. About 5,000 Confederate dead are at Cedar Hill, with 3,400 of those unknown.

Since the National Cemetery closed in 1961, 109 more people have been buried there, and about 50 reservations for plots remain.

Vicksburg played a crucial role for the Confederacy in the Civil War, holding control of the Mississippi River. It surrendered to Union forces after a three-month siege on July 4, 1863.

“We are trying to be very respectful of these final resting places,” Madell said. “That is why we are using research methods that do not physically disturb them.”