Vincent Smothers thought that it would be a job like any other. In the summer of 2007, he told me, his friend Marzell Black asked him for a gun for his mother’s boyfriend. Smothers didn’t sell guns, and he told him so. A few months later, Marzell amended his request, saying, “That dude who was looking for a gun? He asked me how much he would have to pay to kill somebody.” A murder Smothers could handle. “Marzell wasn’t the killing type,” he said. “I told him, ‘That’s not something for you to do. I’ll talk to him and see what this is all about.’ ”