Conversation so far:
Where was Mary Surratt buried?
Mary Surratt was buried in Mount Olivet Cemetery in Washington, D.C., on February 9, 1869.
What did Mary Surratt die of?
Mary Surratt was hanged.
Was Mary Surratt also sentenced to death?
Mary Surratt was sentenced to death.

Question: what prison did this occur in?
Self-contained rewrite: What prison did Mary Surratt's hanging occur?