The National Park Service has described the Petersburg National Battlefield, just south of Richmond, Virginia, as “an active crime scene” after a string of excavations there, CNN reported. Authorities suspect looters were responsible for damage at the site of the Civil War’s longest siege.

“Thieves were likely looking for relics on a field where more than 1,000 Union and Confederate soldiers died fighting during the Siege of Petersburg,” the park service said in a statement.

The service is investigating the alleged looting that was carried out shortly before Memorial Day, which honors those in the armed forces who died serving the U.S.

“This is an affront to the memory of people who fought and died on this field, and it is destruction and theft of history from the American people,” Petersburg National Battlefield Superintendent Lewis Rogers said in a statement. “This kind of aberrant behavior is always disgusting, but it is particularly egregious as Memorial Day weekend arrives, a time when we honor the memories of our friends and family.”

The areas of the battlefield that were affected by the excavations constitute a crime scene, but the rest of the 2,700-acre park remains open to visitors. The digging was reportedly limited to the eastern section of the park. Marked graves were left untouched, according to CNN.

“Earlier this week, one of the park employees was out doing landscape work and noticed some things were out of place,” CNN quoted park representative Chris Bryce as saying. “Many of the holes were just left open. ... They were several inches deep in most cases.”

Looting the battlefield is federal crime, punishable by a fine as much as $20,000 or imprisonment as long as two years, according to the park service, which noted that only 14 percent of such cases are typically solved.

“There’s a market for these items related to the Civil War,” Bryce told the Military Times

Civil War relics such as uniform buttons and rifle parts frequently appear at online auction sites, according to the Washington Post. The 10-month siege of Petersburg pitted Union Gen. Ulysses S. Grant against Confederate Gen. Robert E. Lee, and the Post reported that “excavations occurred where significant fighting took place in June 1864 and March 1865.”

battlefield A member of President Lincoln’s Own Band walks to his seat before the commemoration of the 150th anniversary of the Gettysburg Address at the Soldiers’ National Cemetery at Gettysburg National Military Park in Gettysburg, Pennsylvania, Nov. 19, 2013. Photo: Patrick Smith/Getty Images