Portland police on Monday released a report written by a lieutenant who said he “firmly believed’’ that a milkshake thrown at protesters during competing demonstrations last month in downtown Portland contained a concrete-type substance.

Police put out a warning on Twitter during the June 29 protests that the bureau had “received information” that some of the milkshakes contained quick-drying cement. The announcement spurred widespread backlash, including death threats against the milkshake makers, who said the only ingredients were coconut ice cream, cashew milk and rainbow sprinkles.

PopMob, short for Popular Mobilization, organized the milkshake party in Lownsdale Square, saying its goal was to stage a counterprotest against the right-wing Proud Boys and #HimToo movement.

Lt. Richard A. Stainbrook, one of the commanders of a Rapid Response Team tasked with crowd control, said he was at the intersection of Southwest Morrison Street and Sixth Avenue when a cup of milkshake was thrown at two men at the corner.

He said in his report that an unknown woman approached him as he directed two officers to take a report from the victims.

She told him, “Those things are filled with QUIKRETE,’’ Stainbrook said in his report written July 1, the Monday after the Saturday demonstrations.

The woman’s head and shoulders were covered with a gray-colored substance that was starting to dry, Stainbrook wrote.

“I have worked with concrete periodically and specifically ‘QUIKRETE,’ which is pre-mixed concrete, specifically many times,’’ the lieutenant wrote in his report, obtained through a public records request.

“The substance on the female smelled like ‘QUIKRETE.’ I also noticed as the substance was drying it was turning into a chalky consistency which from my experience is consistent with drying concrete.’’

The woman walked away, he said, before he could direct an officer to take a report from her.

Stainbrook said he also noticed some of the substance on the ground was drying quickly and “turning to a chalky consistency.’’

“I firmly believe these ‘Milk Shakes’ that were being thrown around and on people contained some form of concrete,’’ he wrote. “For situational awareness purposes, I broadcast over my radio that the ‘Milk Shakes’ being thrown around contained Quikrete.’’

Quikrete is a mixture of gravel, sand and cement often used for building or fixing foundation walls, sidewalks, curbs, steps and ramps and for setting posts.

The bureau found no other evidence that the shakes contained any concrete material, receiving scorn for publicizing such information.

Police Chief Danielle Outlaw has said the bureau shared the information “in good faith.’’

"As we get information, we want to alert the public,'' Outlaw said after the protests. "There were no ill intentions whatsoever.''

Attorney Juan C. Chavez, of the Oregon Justice Resource Center, sent a letter to the city July 15 on behalf of (Pop)ular (Mob)ilization or "Pop Mob,'' demanding the police retract the Twitter message within two weeks, arguing that it was "defamatory.'' If no retraction was offered, Chavez threatened to sue the city on behalf of Pop Mob, alleging negligence, defamation and emotional distress.

"They did not put quick-drying cement in their beverages,'' he wrote. "Not only would be be antithetical to Pop Mob’s stated goal of creating a joyful atmosphere, putting a foreign substance into their drink and serving them to counter-demonstrators would likely violate the criminal code.''

City Attorney Tracey Reeve responded, as reported by Portland Mercury, that the Twitter message "accurately stated that the police had ‘received information’ that some of the milkshakes being thrown contained quick-drying cement....The Tweet in question referred to only ‘some of the milkshakes being thrown today.' ''

Reeve said police did not allege wrongdoing by any individuals or group, and she encouraged Pop Mob members who have received harassing threats as a result to report them to police.

-- Maxine Bernstein

Email at mbernstein@oregonian.com

Follow on Twitter @maxoregonian

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