Former Acting Attorney General Sally Yates, seen in 2017, had been selected to lead an investigation into ketamine use during Minneapolis police calls. (Associated Press/The Minnesota Star Tribune)

A new memo from former Acting U.S. Attorney General Sally Yates raises fresh questions about how closely Minneapolis police officers urged paramedics to sedate members of the public.

The preliminary report found 10 instances in which officers showed "a high degree of familiarity" with the powerful sedative ketamine, many of them expecting that simply calling paramedics would result in a person being sedated. Officers then took a "concerning level of participation in conversations with EMS regarding" injecting people with ketamine during emergency calls.

In the memo and other communications with city officials, Yates lamented that the City Council cut her firm's investigation short last summer after determining the $195,000 fee was too expensive. The city paid the firm $50,000 for the preliminary findings.

The memo is dated Feb. 1. It was given to City Council members Wednesday.

"We respect the City Council's discretion to disapprove the contract," wrote Yates in an October e-mail to city attorney Susan Segal. "We nonetheless are disappointed that our engagement will terminate without resolution and that so many of these important questions will remain unanswered."

The report also offers eight recommendations for how to answer some of these questions and improve practices, including interviewing officers on their motivations for asking for ketamine, analyzing ketamine use in Minneapolis police encounters compared to other cities and providing training to officers.

From July to September, the Atlanta-based firm where Yates works, King & Spalding, spent about 427 hours examining materials from 132 police encounters, including 122 hours of video, that took place from 2016 to 2018 and included the term "ketamine" in police reports, according to a letter from Yates. Some of the videos show people being uncooperative or aggressive toward the officers, many with signs of severe mental illness. In the majority of cases, the report said, officers acted professionally, even when dealing with difficult people.

Yet in a significant number of cases involving ketamine, the officers also diagnosed patients with "excited delirium syndrome," according to the report. Excited delirium is a controversial term among medical authorities that describes a form of potentially fatal severe agitation, and its prevalence and even its existence are a matter of debate. The Yates report says that some patients did not always show obvious signs of such a high level of agitation, and investigators found no evidence that police were trained to identify the condition.

The report also notes the mention of ketamine in police reports grew from three in 2012 to 62 in 2017, citing numbers from a Minneapolis civil rights report.

Yates and her colleagues cited questions they say warrant more investigation, including:

• Did a Hennepin Healthcare study on ketamine drive up the use of the drug?

• Is the increase linked to officers being informally instructed on the term "excited delirium?"

• Does the rise signal a new trend in police-citizen encounters?

• Are sedatives used as frequently in police encounters in cities outside Minneapolis?

• Is the increase linked to training or informal practices arising in organizations?

• Are there proper procedures in place for when police request paramedics to join them on scene?

In an interview Thursday, Mayor Jacob Frey and Chief Medaria Arradondo said they shared Yates' disappointment over the council decision to cut short the contract.

"There are clearly still several unanswered questions," said Frey.

After seeing public unrest over revelations that police urged paramedics to sedate people, both city leaders believed they needed to bring an outsider to help earn back public trust, said Arradondo

"We wanted to make sure that there was a respected and credible individual that could come in and do a thorough examination," he said. "I absolutely felt very confident about Ms. Yates' work."

Arradondo said the police department will begin to incorporate the recommendations in Yates' report.

City Council President Lisa Bender said the new report validates the importance of the internal city report completed last summer by the Office of Police Conduct Review.

"I certainly stand by my decision not to have gone forward with $200,000 of city funding for the full report, because I stand by the work that the civil rights department did," she said.

Bender said she's started following up on some of the recommendations in the Yates report. The council and city staff will continue working to shape its policies in order to keep residents safe, she said.

"This is a serious issue that is related to a bigger issue around how MPD officers are interacting with the public and how EMS personnel are interacting with the public," Bender said. "I don't see this memo being the end of that conversation."