Michael Brown, the unarmed 18-year-old whose shooting by a police officer set off more than a week of unrest in Ferguson, Mo., was struck by at least six bullets, including two to the head, according to a former New York City medical examiner.

The autopsy results came as a march protesting Mr. Brown's Aug. 9 death erupted in chaos Sunday night when police forced back demonstrators in a cloud of smoke and a hail of sizzling canisters.

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