Protesters hold signs and chant "Hands up. Don't Shoot" during a protest against the police in Ferguson, Missouri, in the Manhattan borough of New York, Aug 18, 2014. [Photo/Agencies]

Darren Wilson, 28, the officer who shot Brown as the teenager was walking through a Ferguson residential neighborhood on Aug 9 with a friend, was put on paid administrative leave and is in hiding.

Edward Magee, a spokesman for the St. Louis County prosecutor's office, said the case could be presented this week to a grand jury, which will decide whether Wilson will be indicted.

The National Bar Association, the country's largest network of black attorneys and judges, filed a lawsuit on Monday against the city of Ferguson and its police department over evidence related to Brown's shooting.

The suit asks the department to preserve all videos, photographs, police logs and investigative reports about the shooting, as well as arrest reports for protesters who were detained in the days and nights that followed.

The shooting set off protests in Ferguson, whose population of about 21,000 is mostly black. Thousands of demonstrators, angry that the police officer was not arrested, have filled the streets.

The protests have been marred by rioting and looting, leaving some stores badly damaged, as well as attacks against police with Molotov cocktails, officials said.

Law enforcement officials have been widely criticized for using excessive force. UN Secretary-General Ban Ki-moon urged US authorities to protect protesters' rights to peaceful assembly and freedom of expression.

According to accounts by local police, Brown and a friend were walking down a road when Wilson asked them to move onto the sidewalk. Wilson reported that Brown reached into his patrol car and struggled for his service gun when the officer fired the initial shot.

Brown's friend Dorian Johnson, 22, said Wilson had reached out through his car window to grab at Brown and the teenager was trying to get away when he was shot. Johnson said Brown held up his hands to surrender but that Wilson got out of his patrol car and shot him several more times.