Published: Sep 15, 2010 7:42 PM EDT
Updated: Sep 15, 2010 4:42 PM EDT

WASHINGTON (AP) - Arlington National Cemetery has discovered three people buried in the wrong graves.

The Army said Wednesday that officials opened three burial sites last month and found that the remains in each had been interred in mismarked graves.

The discovery follows an investigation into bookkeeping problems and burial mix-ups at Arlington, one of the nation's most hallowed sites.

At the request of his father, the grave and casket of Marine Pfc. Heath Warner of Canton, Ohio, was opened on Wednesday. That grave was found to hold the remains of Warner, who was killed in Iraq in 2006.

Army spokesman Gary Tallman says he's not aware of any other family requests for exhumations.

Officials say up to 6,600 graves might be unmarked or mislabeled on cemetery maps.