Ever since the document was examined several weeks ago, it's been a mystery.

Initially, it appeared to be a reproduction of the terms and conditions of Confederate Gen. Robert E. Lee's surrender in Appomattox, Va., in 1865.

But staff members of the Civil War and Underground Railroad Museum in Center City - who came upon the document while preparing for the museum's relocation - soon noticed pen indentations in the paper, and darker and lighter ink strokes consistent with handwriting.

They also found a notation in a 1935 museum inventory identifying the document as an "original."

Could this artifact, crudely varnished and glued to cardboard, be one of the three known originals of the historic surrender terms?

Or is it a souvenir or military field copy produced and signed later?

Those are the questions historians and curators are now trying to answer. The discovery of Lee's missing copy would be a tremendous discovery for Civil War historians.

There were no clear answers yesterday, only a deepening mystery as experts compared the museum's find to a verified original in the collection of the Maryland Historical Society.

The handwriting and spacing of the two appear to be identical.

But if the Philadelphia find isn't an original, why do the ink strokes appear uneven? asked museum curator Andrew Coldren. And would it have scratchy pen marks?

"It's remarkable and intriguing," Coldren said. The documents from the Maryland Historical Society and the Pine Street museum, which closed Saturday, "look almost the same."

The comparison "raises more questions than it answers, but that's typical when dealing with historical documents. We're going to have to do more research," he said.

Coldren hopes the museum can obtain funds to preserve its surrender document, then compare it more closely with the original in Maryland. He was checking it against a computer-scanned facsimile from Baltimore yesterday.

"There are authentic signatures on the paper," Coldren said of the museum's find. "We have an original document of some kind, but we don't want to make claims about it. It's important to be skeptical."

The surrender terms were worked out by three Union and three Confederate generals on April 10, 1865, the day after Lee and Union Gen. Ulysses S. Grant agreed on the broad issues.

Three copies were made, according to the memoirs of Union Gen. John Gibbon, who was placed in charge of working out the details. Gibbon's went to the Maryland Historical Society and Grant's went to the National Archives. Lee's has been missing.

"There was disarray of official Confederate documents after the war," said Civil War museum president and chief executive officer Sharon Smith. "There are a lot of reasons why Lee's copy could have been lost."

The museum's document was donated by Bruce Ford, a well-to-do businessman whose father was a Union veteran. Ford joined the group that formed the museum in 1917.

His document was examined recently as museum workers pulled artifacts out of storage and reevaluated them in preparation for a move to a new museum site at the First Bank of the United States, near Third and Chestnut Streets. The museum is expected to open there in 2010.

"It's unfortunate the provenance doesn't go back further," said Patrick A. Schroeder, a historian at Appomattox Court House National Historical Park. "That's why it's hard to say what the Philadelphia copy is."

Though three official copies existed, Schroeder said, duplicates may have been produced to share with commanders in the field or to keep as souvenirs. He also said the military may have used a "two-pen" machine to make copies.

"It's pretty neat whatever it turns out to be," Schroeder said.

Contact staff writer Edward Colimore at 856-779-3833 or ecolimore@phillynews.com.