By Scott Malone and Ellen Wulfhorst FERGUSON Mo. (Reuters) – U.S. Attorney General Eric Holder was visiting Ferguson, Missouri, on Wednesday, hours after nearly 50 protesters were arrested in the 11th straight night of demonstrations over the killing of an unarmed black teenager by a white police officer. The St. Louis County prosecutor’s office will also begin presenting evidence on Wednesday to a regularly seated grand jury investigating the August 9 shooting death of 18-year-old Michael Brown. Prosecuting attorney Bob McCulloch said his office could continue presenting evidence to the grand jury through mid-October as he confronts conflicting pressures for speed and thoroughness. “On one side, people are saying you’re rushing to justice, and on the other side, they’re saying you’re dragging this thing out,” he said at a news conference.