(This is the second article of a two-part series. Part 1 ran May 19.)On Aug. 1, 1942, after one of them had been beaten up, members of the 38th Street Club returned to Sleepy Lagoon, a reservoir along the Los Angeles River popular with Mexican Americans, to find the perpetrators for payback. The next day, Jose Diaz, was found dead.This is the setting for Eduardo Obregón Pagán’s book, “Murder at the Sleepy Lagoon — Zoot Suits, Race, and Riot in Wartime L.A.,” the retelling of the notorious Sleepy …