Last December, 20-year-old Dakota Reed drew the attention of American law enforcement after he posted troubling threats on the internet, claiming a plan for mass slaughter.Just two weeks after a shooting at a Pittsburgh synagogue left 11 people dead, Reed appeared to promise to carry on in the dark American tradition of violence, in a post on one of seven Facebook accounts he apparently kept, and used to spread hateful messages. “I’m shooting for 30 Jews,” he wrote.