On July 10, at 4:19 a.m., gunfire was detected in the District's Bloomingdale neighborhood. Not five minutes later, police found Seth Rich, a 27-year-old Democratic National Committee staffer, lying on the ground, dying from a bullet wound to his back. A conscious Rich was transported to the hospital; by daybreak, he was dead.Nearly one year later, Rich's death remains one of America's thousands of unsolved murders — and the focus of endless conspiracy theories, spread this past week by Fox News, alt-right social media, a local D.C. news station and the Russian embassy in Britain. The reemergence of the conspiracy...