'I'm not going anywhere,' rapped a defiant MS-13 gang member. Days later, he was dead.

Christian Sosa Rivas knew he was a marked man. The brash, 21-year-old leader of an MS-13 clique in Springfield, Virginia, had incurred the wrath of rivals in the violent street gang. So in late 2016, the aspiring rapper sat in the back of a dimly lit car and recorded what would be his last music...