The evidence of guilt is not open to question. Jahar Tsarnaev's attorneys conceded he helped plant the bombs that killed three and injured 260. Now the jury that convicted him must decide the sentence. But even the families of victims disagree. Some insist only his death will provide closure. Others say his execution would inevitably be delayed by an endless round of appeals, prolonging their agony. Opening arguments began today in the penalty phase of a trial that raises basic questions about justice in America.