I came across this story when visiting Antietam Battlefield this weekend.
Apparently, 2 years ago, a visitor discovered human bone fragments at the entrance of a groundhog burrow in the area of The Cornfield. He reported the find to Park Rangers, and the battlefield site from 140 plus years ago was excavated to look for clues as to the soldier's identity.
His remains were returned and reinterred in his home state of New York on the Anniversary of the Battle in 2009.
Our national responsibility to our fallen heroes never expires...