Portland police shouldn't detain groups of people or make mass arrests without a compelling government interest to protect life or property and a written policy guiding their actions, a police oversight office says in a new report released Thursday.

Officers had neither legal justification nor any policies to support their decision last June 4 to kettle -- encircle and stop -- nearly 400 counter-protesters during a Patriot Prayer rally in downtown, Independent Police Review officials said.

The report follows 27 separate citizen complaints, many that criticized the police tactics that swept up innocent bystanders.

It also comes as a federal lawsuit filed by the American Civil Liberties Union of Oregon and others is pending against the city, the mayor and police, accusing them of violating free speech rights by unlawfully corralling hundreds of protesters without probable cause.

During the June 4 rally and counter-protests, police detained and photographed 389 people and demanded to see and photograph their identification without any intelligence-gathering purpose or plan on how police would use, share or retain the photos, the report found.

Though then-Police Chief Mike Marshman said the bureau would purge photos if people weren't part of a criminal investigation, it still has the photos and pictures of IDs, the review office investigators found.

The reviewers also recommended that police not detain legal observers and the media, who got caught up in the crowd held nearly a year ago.

Police also should retain audio recordings of officers' discussions on encrypted radio channels during responses to large demonstrations or protests, the oversight staff noted. Those recordings now aren't preserved.

"As a result, Police Bureau managers and other reviewers are deprived of a critical contemporaneous record,'' the report said. Other police agencies keep all radio transmissions of crowd control events, investigators said.

In a written response, the Police Bureau agreed that mass detentions should come only in a "extraordinary circumstances'' and at the direction of an incident commander.

The bureau is writing guidelines for mass detentions and expects to have a draft for public review by July. Police must have probable cause to arrest each individual in mass arrests, the bureau said. Police also will consult with the city attorney's office to develop guidelines on what to do with photos taken of people detained but not arrested.

The bureau, however, doesn't believe it should keep the encrypted radio talk for review. The "sensitive discussions," which include observations of criminal behavior and tactics, "would be detrimental to the safety of both officers and the public,'' the bureau said.

The ACLU and five plaintiffs successfully sought a judge's order to allow their case in federal court to become a class-action, noting that police held hundreds of people, including peaceful protesters, bystanders and media, on Southwest Fourth Avenue, between Morrison and Alder streets, for almost an hour.

People in the group were allowed to leave only after police photographed them and their ID, an unlawful detention without reasonable suspicion, wrote attorney Steven Wilker, one of the attorneys for the ACLU of Oregon. U.S. Magistrate Judge Paul Papak granted the class action classification Thursday.

City attorneys said they don't object to the class action. In court documents, police acknowledge they corralled a throng of marchers, took their photos and demanded their IDs, but say they moved in only after people ignored repeated announcements by officers to leave or because they needed to investigate disorderly conduct.

-- Maxine Bernstein

mbernstein@oregonian.com

503-221-8212

@maxoregonian