The parents of fallen Indianapolis police Officer David Moore made a heartbreaking discovery at his grave this weekend.Spencer Moore stopped by Crown Hill Cemetery on Saturday to find that several mementoes placed on his son's final resting spot were missing.The items included challenge coins commonly exchanged by military and law enforcement officers and a set of Marine Corp medals left by Moore's best friend."They have no real value on the economic scale, but they have a lot of value on the heart scale," Spencer Moore said. "Some, like the challenge coins that people would lay there, you can see there are rings left where they were taken. These are exchanged by friends to commemorate that friendship."David Moore was killed in the line of duty in January 2011.The family is asking whoever took the items to please return them to their son's grave.