Four American presidents have been assassinated, but only one city has ever been blamed for an act of political murder: Dallas.

The arrest of perhaps the only proud Marxist within a 100-mile radius of Dealey Plaza did little to placate those who believed that Dallas’ atmosphere was somehow responsible. The story of how the city subsequently coped with America’s emotional Grand Canyon should be one of the feel-good stories on the 50th anniversary of the assassination except for one thing: How Dallas has inaccurately portrayed what happened that day in Dealey Plaza.

Until 2013, Dallas desisted from erecting interpretive graphics. The only commentary was a plaque affixed in 1981 to the former Texas School Book Depository. Included in the plaque’s inscription is the note that Oswald “allegedly” killed JFK. This unwise concession to conspiracy theorists illustrates the depth of Dallas’ trauma; long before the Warren Commission report, the city’s own lawmen knew they had apprehended the right killer.

Otherwise, Dealey Plaza was frozen in time. Visitors were left to marvel at how small an area it really is, compared to the enormity of the crime....