The American Civil Liberties Union (ACLU) of Missouri on Friday filed a lawsuit against the city of St. Louis alleging police officers engaged in "unlawful and unconstitutional actions" against demonstrators protesting the acquittal of a white former police officer in the death of a black motorist.

The lawsuit accused police of improperly using chemical weapons, interfering with video of police activity and unlawfully detaining protesters at a Sunday demonstration when officers used a tactic called "kettling" to corral protesters.

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The ACLU of Missouri filed the lawsuit on behalf of two women — Maleeha Ahmad and Alison Dreith — who participated in the protests. Both women were allegedly sprayed in the face with pepper spray without warning on Sept. 15.

Last week, a judge found former police officer Jason Stockley not guilty of murder in the 2011 shooting death of Anthony Lamar Smith, touching off days of protest in downtown St. Louis.

Stockley shot Smith after a high-speed chase. According to a court document, the police officer was heard saying during the chase that he was "going to kill this motherf---er, don't you know it."

The former officer said Smith was holding a gun, but only Stockley's DNA was found on the weapon. Prosecutors allege that he planted the gun.

Police have arrested more than 160 protesters since demonstrations began on Sept. 15.

A hundred twenty people were arrested Sunday night during a demonstration in downtown St. Louis, when police used "kettling" — a method of grouping protestors in a small area for crowd control — to box in protesters.

Police had previously ordered protesters to disperse. But many people argued that they were unable to leave the area, because police had effectively blocked them from doing so, consequently leading to the arrests.