Since its creation in 1982, the Vietnam Veterans Memorial has become the most visited National Park Services site. Each year, 4.5 million people come to the Wall. Many of them leave letters or other special objects. Every night, park rangers collect and inventory these mementos—now numbering well over 90,000—and put them into government storage.Michael Sofarelli, the son of a Vietnam War veteran, has combed through the archives searching for the most gripping letters and objects: a...