These 3-foot-high walls bear the names of 20,267 American police officers killed in the line of duty since 1791. On the third line of panel 13W are the names of six officers killed by William Bonney, better known as Billy the Kid. J. D. Tippit, the Dallas policeman killed by Lee Harvey Oswald, is honored on the ninth line of panel 63E. Other names include the 72 officers who died due to the events of 9/11. Directories there allow you to look up officers by name, date of death, state, and department. Call to arrange for a free tour. A National Law Enforcement Museum is in the works; until then, a small visitor center (400 7th St.) has a computer for looking up names, a display on the history of law enforcement, and a small gift shop.