When the government released the bodies of the Lincoln conspirators to their families in 1869, there was one condition. None of the four persons hanged on July 7, 1865, could have a marked grave.
Davy Herold’s body was laid to rest hear his father’s body in Congressional Cemetery in Southeast Washington, D.C. The Herold family figured out a way to circumvent the ban on marked graves for conspirators.
When Davy’s sister died, they buried her on top of Davy’s coffin, so they would always know where he was.
Source: The Lincoln Assassination: Where Are They Now? A Guide to the Burial Places of Individuals Connected to the Lincoln Assassination in Washington, D.C. by Jim Garrett and Richard Smyth