Ferguson, Missouri (CNN) -- The FBI has officially opened an investigation into the shooting of a teenager by a police officer in the St. Louis suburb of Ferguson, Missouri, a U.S. law enforcement official tells CNN.
Federal investigators are joining the U.S. Department of Justice in assisting local authorities to garner the facts surrounding the killing of 18-year-old Michael Brown, who was shot Saturday night.
Tensions have been high in the town of 21,000. Dozens took the streets Monday to march and chant, "No justice, no peace!" A vigil for the teen devolved into chaos Sunday when violence and looting broke out among protesters.
Witnesses to Brown's shooting said he had been unarmed and had his hands in the air.
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