A member of the grand jury that declined to indict the white Missouri police officer who fatally shot an unarmed black 18-year-old sued the prosecutor in the case on Monday, criticising the way evidence was presented to grand jurors and seeking court permission to speak publicly about the way the case was handled.

The lawsuit was filed in federal court in St Louis against St. Louis County prosecutor Robert McCulloch by the grand juror, whose name was withheld and was referred to as "Grand Juror Doe".

The lawsuit relates to the August 9 shooting of Michael Brown by officer Darren Wilson in the St Louis suburb of Ferguson. Brown's death and the grand jury's decision not to indict Wilson triggered months of protests over police treatment of African-Americans in the United States.

The suit argues that state laws prohibiting the grand juror from talking about the case are unconstitutional. Jeffrey Mittman, executive director of the American Civil Liberties Union in Missouri, said the Brown case is an important public policy issue and the grand juror should be allowed to speak about the proceedings.

After the November 24 announcement by McCulloch that the grand jury decided not to indict Wilson, and the release by McCulloch of evidence presented, some critics accused the prosecutor of unfairly skewing the process in favor of the police officer.

A spokesman said McCulloch had no comment on the lawsuit.

The lawsuit claims that evidence was presented to the grand jury in a manner markedly different than in previous cases heard by the same grand jury, with the "insinuation" that Brown was the "wrongdoer" rather than Wilson.

It also claims the prosecutor's office presented applicable laws to grand jurors "in a muddled and untimely manner" unlike presentations in other cases.

The grand juror also contends that McCulloch's public statements about the decision not to indict were not "entirely accurate," including the "implication that all grand jurors believed that there was no support for any charges," the lawsuit stated.

The grand jury in the case began meeting in May for a term originally scheduled to conclude in September. But that term was extended so the jurors could take up the Brown shooting.

Lawyers for Brown's family and some witnesses say he was trying to surrender when Wilson shot him multiple times. Wilson's supporters say the officer feared for his life and fired at Brown in self-defence.