The Federal Bureau of Investigation will open a parallel inquiry into the shooting death of 18-year-old Michael Brown by a St. Louis-area police officer, local police announced Monday. "At every step, we will work with the local investigators, who should be prepared to complete a thorough, fair investigation in their own right," Attorney General Eric Holder said in a statement. Brown’s death sparked protests that turned violent late Sunday. Gas stations and businesses were looted and police say that at least 20 patrol cars were damaged. According to one officer, the use of tear gas against demonstrators is now a possibility. According to witnesses and friends, Brown was unarmed and had his hands in the air when a police officer shot and killed him Saturday afternoon—though that account is disputed. “The genesis of this was a physical confrontation,” said Jon Belmar, chief of the St. Louis County Police Department. According to Belmar, Brown pushed an officer back into his car, “where he physically assaulted the police officer” and struggled to gain hold of the officer’s weapon.