City Prison, built in late 1830s and called the Tombs because of its mausoleum  design, was where NYC executions took place. All 18 previous to Feb. 21, 1862, had been under state law. The hanging on that date was a federal case: Maine Capt. Nathaniel Gordon, the first and only U.S. slave trader ever executed.  Why was the City Prison chosen for the federal execution (depicted in Harpers magazine illustration).
The image of the Tombs execution of Nathaniel Gordon is based on one appearing on the HarpWeek web site at