Letters written by early presidents, a famous explorer, and the Confederacy’s leader will be returned soon to the Filson Historical Society, and the 70-year-old history buff who admitted pilfering them is facing possible prison time.

Donald Eckard Sr. of Louisville pleaded guilty in federal court on Thursday to eight felony counts of art theft. He admitted that on four visits to the Filson Society, he stole the eight letters—the oldest of which were penned by Thomas Jefferson and date back to the late 1790s.

Each letter is valued at more than $5,000, the minimum amount needed for the charges.

The letters were written by Jefferson and two other presidents—

John Quincy Adams and Andrew Jackson—as well as by explorer William Clark and Confederate President Jefferson Davis.

Richard H.C. Clay, an attorney for the Filson Society, said the letters were “classic expressions of United States history,” and some had “direct bearing on Kentucky history.”

“In some instances, the documents will refer to specific instances in American history,” Clay said in an interview Friday. “But in many, they are simply fascinating indications of the thinking of these famous individuals on everyday matters.”

Some documents had minimal damage but can be restored, Clay said. The Filson’s insurer has agreed to pay for restoration, estimated at about $91,000, he said.

As part of his plea, Eckard agreed to pay $91,763 in restitution, Assistant U.S. Attorney Hancy Jones III said Friday. Both sides agreed that federal sentencing guidelines applicable in the case could lead to a possible prison sentence of about three years, he said.

Sentencing was set for April 13 in U.S. District Court.

Eckard’s attorney, Michael Mazzoli, declined comment through an employee at his law office.

The letters were stolen between July 25, 2003 and Aug. 3, 2004, prosecutors said.

The FBI found the letters at Eckard’s home, where some were framed and hanging on a wall. Clay said there was no indication that Eckard tried to sell any of the letters.

The letters will be returned to the Filson after Eckard’s sentencing, Clay said.

Eckard used a false name when signing in to review the artifacts, Clay said. A surveillance camera showed Eckard pilfering a letter, prompting the Filson to contact the FBI, he said.

Clay said the Filson has since strengthened security for its collection of artifacts.