Ezequiel Romo had been gone a long time. He went to prison in 1996. When he returned to Panorama City 18 years later, he didn't like what he saw. He was going to "clean out house," Romo told another veteran of his gang. He would rid the neighborhood of rivals, of informants, of drug addicts and the do-nothings he considered dead weight. Prosecutors said the 45-year-old made good on that promise: On Romo's orders, members of his gang, Blythe Street, turned on and killed one another in a string of murders that left eight dead, according to evidence presented at...