Committed during a period filled with bombings, killings, and disappearances, the murder of Jean McConville remains one of the most infamous unsolved crimes of the Troubles. The writer Patrick Radden Keefe may have discovered who killed her. Plus, the costume designer Ruth E. Carter, best known for her work on the movie “Black Panther,” talks about her decades-long career. And The New Yorker presents the second year of the Brody Awards.