Thomas Jackson, the police chief of Ferguson, Missouri, made the announcement in front of a gas station that was burned during the demonstrations.
Michael Brown, 18, was shot to death during a confrontation with the officer on Saturday afternoon. Police have withheld most details about the encounter, including the number of bullets that hit Brown.
Jackson had declined for days to release the name of the officer, citing threats issued on social media.
The unrest escalated and peaked on Wednesday night, when police fired tear gas into crowds of protesters. Police were criticized for a military-style presence that included officers atop armored trucks aiming rifles at crowds.
Relative calm was restored Thursday night after Missouri Gov. Jay Nixon put the state Highway Patrol in command.
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