GRAND RAPIDS, Mich. (AP) — A 19-year-old man suspected of defacing the gravesite of former President Gerald Ford and first lady Betty Ford has pleaded not guilty to misdemeanor charges.

The Grand Rapids Press reports Christian Johnson entered the plea Monday to charges of larceny and malicious destruction of property of tombs or memorials.

Police have said Johnson and a female co-defendant turned themselves in after the March 27 incident and returned a missing letter. Johnson has apologized, saying he didn’t know what the gravesite was.

The co-defendant bonded out of jail Monday and has not yet been arraigned. She faces a misdemeanor count of receiving and concealing stolen property valued at less than $200.

The Fords are buried outside a Grand Rapids museum dedicated to Gerald Ford’s presidency. It currently features an exhibition of photography by President Gerald Ford’s personal White House photographer, David Hume Kennerly.