Emotions ran high at Manhattan criminal court on Monday, after the jury read the not guilty verdict in the polarizing trial of Daniel Penny, the Marine veteran accused of killing a Michael Jackson impersonator, Jordan Neely, on a New York subway last year. Outside the courthouse, one protester, angry at the verdict, was arrested by the police. Black Lives Matter activists advocated for “Black vigilantes” to retaliate. Meanwhile, Mr. Penny was enjoying a celebratory drink with his attorneys at a downtown bar.