CHARLESTON, S.C. — Dylann Roof was convicted Thursday in the chilling slaughter of nine black church members who had welcomed him to their Bible study, a devastating crime in a country that was already deeply embroiled in racial tension.The same federal jury that found Roof guilty of all 33 counts will reconvene next month to hear more testimony and weigh whether to sentence him to death. As the verdict was read, Roof just stared ahead, much as he did the entire trial. Family members of victims held hands and squeezed one another's arms.