Updated Nov. 15 at 2:00 p.m. with comments from ACLU, Mayor Krewson — A federal judge has ordered the St. Louis Metropolitan Police Department to alter tactics its officers use to respond to protests, especially demonstrations aimed at changing law enforcement policies.

In a 49-page opinion issued Wednesday, U.S. District Judge Catherine Perry blocked the department from ordering protesters to disperse unless there’s an immediate threat of violence. Perry also limited when officers can use chemical agents like pepper spray or mace.

The ACLU of Missouri filed suit Sept. 22 on behalf of Maleeha Ahmad and Alison Dreith, two women who were pepper-sprayed while engaging in a peaceful protest on Sept. 17. That’s two days after a St. Louis judge found a white former police officer not guilty of first-degree murder in the 2011 shooting death of a black man.

The ACLU alleged the department violated the civil rights of protesters by not giving them a way to leave once a dispersal order had been given. The lawsuit also accused the officers of using pepper spray and other chemical agents in retaliation for protests.

Judge Perry ruled that if the case goes to trial, the ACLU is likely to be able to prove that “the policies or customs of defendants … violate the constitutional rights” of protesters.

“If St. Louis is to address its long-standing racial inequities, the community must be able to safely express its outrage and pain through nonviolent freedom of speech,” Jeffrey Mittman, the ACLU’s executive director said in a statement.“We must use this as an opportunity to develop a collaborative approach to policing between the community and law enforcement.”

Mayor Lyda Krewson said in a statement that she “appreciated the time and effort of Judge Perry,” and that the city would comply with the judge’s order.

A second federal lawsuit, filed on behalf of two Kansas City-based filmmakers, has yet to be resolved. A third case that challenged how protesters were treated after they were arrested was dismissed after the judge overseeing the city’s municipal court limited the use of cash bail to certain cases.

New tactics

“The police department has taken the position that any time two people do anything illegal, even if it’s completely non-violent, the police have the discretion to rule the entire assembly unlawful and demand that everyone go home,” said Tony Rothert, the ACLU’s legal director. Perry’s ruling, he said, means that protesters can be ordered to leave a specific area if people are being violent.

“The police can clear the scene of an unlawful assembly, but not demand that all assemblies cease in the city for the rest of the day,” Rothert said.

Perry also ordered the department to stop using chemical munitions in retaliation for protests or for recording the police. Police will only be able to deploy pepper spray or other agents if there’s probable cause to arrest a person and police have issued audible warnings.

The city was already under a federal court order from 2015 that required police to give warnings before using tear gas or other chemicals to disperse a crowd. Rothert said, in his opinion, the department wrongly believed that ruling applied only in those specific circumstances.

Next steps

In an unusual move, Perry immediately ordered the city and the ACLU to sit down and attempt to reach a settlement — something that usually happens when a case is much farther along.

“We didn’t ask for that, but we are happy,” Rothert said. “We think that there are people in leadership in the city of St. Louis who in good faith want to change how policing is done in St. Louis and help restore St. Louis’ reputation as a place where First Amendment rights may flourish.”

Rothert said it was “disturbing” how effective the tactics had been at discouraging people from protesting.

Perry’s decision comes a day after aldermen heard testimony on a bill that would write similar restrictions into law. Court cases and legislation are both important avenues to change the way police act in St. Louis, Mittman said.

Krewson and interim chief Lawrence O’Toole, along with the NAACP Legal Defense Fund, have asked the federal prosecutor in St. Louis to look into how police responded to the demonstrations that started Sept. 15. U.S. Attorney Jeffrey Jensen did not immediately respond to a request for comment.

The executive director of the Civilian Oversight Board, which helps with police discipline, said the board had received eight complaints directly related to verdict protests.

Follow Rachel on Twitter: @rlippmann