A Virginia researcher has confessed to tampering the date on a presidential pardon penned by Abraham Lincoln, making it look as if the pardon was one of the president's final acts - thus changing its historical significance.

On January 12, Thomas Lowry, a long-time Lincoln researcher admitted to altering an Abraham Lincoln presidential pardon for Patrick Murphy, a Civil War soldier in the Union Army who was court-martialed for desertion. Lowry used a fountain pen with a fadeproof, pigment-based ink to change the date, according to National Archives.

Lowry admitted to changing the date of Murphy’s pardon, written in Lincoln’s hand, from April 14, 1864 to April 14, 1865, the day John Wilkes Booth assassinated Lincoln at Ford’s Theatre in Washington.

Having changed the year from 1864 to 1865, Lowry was then able to claim that this pardon was of significant historical relevance because it could be considered one of, if not the final official act by President Lincoln before his assassination.

In 1998, Lowry received national media coverage for his discovery of the Murphy pardon, and the document was exhibited at the National Archives Building in Washington. Lowry cited the altered record in his 1999 book, Don't Shoot That Boy: Abraham Lincoln and Military Justice.

However, Trevor Plante, an archivist at the National Archives, believed the date on the Murphy pardon had been altered: the 5 in 1865 looked like a darker shade of ink than the rest of the date and it looked as if there might have been another number under the 5. Another investigative archivist examined the document and confirmed Plante's suspicions.

Lowry agreed to be interviewed by the National Archives Office of the Inspector General and he eventually admitted on January 12, that he had altered the date.

David Ferriero, archivist of the United States, termed it a criminal intention to rewrite history.

This matter was referred to the Department of Justice (DOJ) for criminal prosecution. However, the DOJ informed the National Archives that the statute of limitations had expired, and therefore Lowry could not be prosecuted.

National Archives says its conservators will examine the document at a later date to determine whether the original date of 1864 can be restored by removing the 5.