Attorney General Eric Holder, on the eve of his visit to Ferguson, Mo., to discuss the police shooting of an unarmed 18-year-old, is urging an end to the violence that has marred some of the protests.

"We understand the need for an independent investigation, and we hope that the independence and thoroughness of our investigation will bring some measure of calm to the tensions in Ferguson,'' Mr. Holder wrote in an op-ed for the St. Louis Post-Dispatch.

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