FERGUSON, Mo. – Protests are continuing in Ferguson, Missouri, over the fatal shooting of a black teenager by a white police officer.

A demonstration quickly deteriorated Sunday night when marchers pushed toward one end of a street.

Police tried to push them back by firing tear gas while shouting over a bullhorn that the protest was no longer peaceful.

Many of the marchers retreated, but a group of about 100 stood defiantly about two blocks away until getting hit by another volley.

Meanwhile, Attorney General Eric Holder has ordered a federal medical examiner to perform another autopsy on the body of 18-year-old Michael Brown.

A Department of Justice spokesman cites a request by family members and the “extraordinary circumstances” surrounding the case in explaining the decision.

The Justice Department already had deepened its civil rights investigation of the shooting.

Officials say 40 FBI agents have been going door-to-door gathering information in the neighbourhood where an unarmed Brown was shot to death in the middle of the street on Aug. 9.