Because "it was the right thing to do."

Robert Thomas, 83, breezed into the National Archives with a smile, a white hankie peeking out of his suit coat pocket and an old briefcase containing the two rare books he filched in Germany 64 years ago.

He was a World War II GI then, fresh from the horrors of combat. He had blundered into one of the notorious salt mines where the Germans stashed their national treasures. And this one contained books. Millions and millions of books from institutions across Germany.

Thomas poked around, saw two that looked old and took them.

Now, a lifetime later, in an ornate room with a fireplace and two chandeliers and the German ambassador looking on, the retired optometrist from Chula Vista, Calif., was returning them.

Everyone seemed happy. Thomas, a widower with two hearing aids who still has a touch of the brash and cheerful GI about him, said he acted because "it was the right thing to do."

He hadn't been bothered that much by keeping the books all these years. Other things haunted him more -- such as the German soldier who looked like a child that Thomas had shot one day in a bunker along the Siegfried Line.

"I've had these books since I was 18 years old," he told a group of officials from the archives Tuesday, as he removed the plastic wrap covering the two boxes in an anteroom before the ceremony. "I'm relieved, for one. I wanted to return them to the original owners, but I had no clue where to start."