Civil War artifacts have been looted from a battlefield, prompting National Park Service authorities to declare the site an “active crime scene,” reported CNN.

Authorities with the National Park Service are investigating a series of looting at the Petersburg National Battlefield, which is just south of Richmond, Virginia and described as the site of the war’s longest siege. The battle, which began in 1864, lasted nine months and claimed 70,000 casualties.

National Park Service spokesman Chris Bryce told CNN a park employee noticed something was amiss at the battlefield that draws some 200,000 visitors annually.

“Earlier this week, one of the park employees was out doing landscape work and noticed some things were out of place.”

A large number of excavated pits were found in the eastern part of the park, the National Park Service said. Marked graves were left undisturbed.

According to Military Times, the looters were likely digging for relics left behind on the field from the more than 1,000 Union and Confederate soldiers who lost their lives fighting during the Siege of Petersburg, which lasted from June 9, 1864, through March 25, 1865.

Noting that “there’s a market for these items related to the Civil War,” looters dug up trenches looking for such artifacts like uniforms buttons, bullets or other similar artifacts, which can be worth a surprising amount on internet auction sites dedicated to Civil War memorabilia.

Park officials are unable to determine what type of items or relics were stolen in the theft because the looters likely got off with previously undiscovered Civil War artifacts.

“They are probably doing their homework of the area, probably did research on Civil War…They were in the ground, they likely would have used a metal detector and a digging tool.”

Looters take Civil War artifacts from Petersburg National Battlefield https://t.co/GjiuOjqdY9 pic.twitter.com/XSf6OFmOB2 — WTVR CBS 6 Richmond (@CBS6) May 28, 2016

According to the Park Service, looting a National Battlefield is a federal crime covered by the Archeological Resources Protection Act of 1979 and carries a fine of up $20,000 and two years in prison, or both, if convicted.

It was on the Civil War battlefield that the siege of Petersburg pitted Union General Ulysses S. Grant against Confederate Gen. Robert E. Lee over supply lines. The lengthy siege eventually led to the fall of the Confederate capital of Richmond, Virginia and was a determining factor in the surrender of the Confederacy.

Looters dig up Petersburg National Battlefield in search of Civil War artifacts. https://t.co/m7279zkmWx pic.twitter.com/kU82MYRpAb — Times-Dispatch (@RTDNEWS) May 28, 2016

Petersburg National Battlefield Superintendent Lewis Rogers denounced the looting in an announcement of the theft.

“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. 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.” “Historians are still writing history based on the archaeological clues left by those who have preceded us. Removing these artifacts erases any chance for us to learn from our nation’s greatest tragedy. Someone may have seen something we need to know.”

Please RT! Thieves steal Civil War relics from Petersburg National Battlefield https://t.co/9eKhwymrqr pic.twitter.com/fLggPYDSFi — WTVR CBS 6 Richmond (@CBS6) May 27, 2016

The public can call in tips on the looting of the Civil War battlefield and are encouraged to call the toll-free number, (888) 653-0009.

This Memorial Day weekend, the affected area on the Civil War battlefield remains an active crime scene, but the remainder of the 2,700-acre park will open to visitors.

(Image via Wikimedia Commons/Muhranoff)