SALT LAKE CITY — A University of Utah law professor has drawn a link between a spike in shooting deaths across several large U.S. cities and changes in policing tied to widespread protests against racial injustice.

Homicides and shooting rates jumped across the country in late May and remained high over the next two months, in large part because police departments reassigned officers to protests or pulled back on patrols, keeping them away from their usual anti-gun efforts, said Paul Cassell, a legal expert and former federal judge.

“Ultimately the big picture explanation of the recent homicide spikes is also the simplest one: Less policing focused on gun crimes as a result of the protests and their fallout produced an increase in gun crimes,” Cassell wrote in the paper set to be published in the Federal Sentencing Reporter. He called the surge in deaths “shocking” and said it requires urgent attention.

Under what he calls “the Minneapolis effect,” Cassell estimates reduced policing led to 710 more homicides and 2,800 more shootings in June and July. Those injured or killed tend to live in low-income neighborhoods and belong to racial and ethnic minority groups.

Cassell analyzed police data from several large cities: Minneapolis, Chicago, Philadelphia, Milwaukee and New York City. Chicago, for example, recorded 107 killings in July, up more than double from the same month a year earlier, he said, and the highest in a single month since September 1992.

The pandemic may play a role in the upticks, but it doesn’t explain them, Cassell said.

This year’s spike did not align with the onset of the coronavirus in March but instead began in late May, when demonstrators took to streets across the nation after a Minneapolis officer pressed his knee to George Floyd’s neck for nearly nine minutes even after Floyd stopped breathing.

Even after protests began to wane, police continued to pull back from “proactive policing,” Cassell wrote, like stopping people on foot or in cars and confiscating guns from those carrying them unlawfully. Some were grappling with budget cuts and hits to morale; others a wave of resignations and early retirements.

Chicago and Philadelphia, however, have since deployed special teams to prevent gun violence in certain areas or respond to protests, Cassell noted.

His theory is similar to the Ferguson effect, the idea favored by many law enforcers that they could not properly do their jobs following public outcry over the 2014 death of Michael Brown, shot by police in Ferguson, Missouri.

Critics have said the notion failed to account for longtime declines in arrests and increases in homicides over several years. Some national studies have refuted the theory, but the wide reviews may obscure phenomena taking place only in certain cities, Cassell said.

Other experts have pointed to distrust of police in certain communities as a potential reason for the increase in shootings and deaths, noting residents may have reported fewer crimes and opted to settle disputes on their own.

But Cassell said the data available in the cities he considered doesn’t support that idea.

A national Gallup poll this summer indicated 86% of adults wanted the same police presence, even though most said they wanted to see major police reforms.

And in Minneapolis, where four officers were charged in Floyd’s killing, there was no substantial dip in police calls to its already overwhelmed 911 system, although it’s not clear whether certain neighborhoods placed fewer calls, Cassell said.

Lex Scott with Black Lives Matter Utah said she’s skeptical of the findings.

“If the murder rate has gone up, it’s definitely not because of Black Lives Matter protests. And if the police are saying, ‘Hey, we aren’t able to control the murder rate because we have to be at these protests,’ I would argue and say, ‘You don’t have to be at these protests. Your presence there makes the situation more dangerous and volatile for everyone,’” Scott said.

When police are absent, Scott said, the gatherings remain lighthearted. She said she shared similar concerns with representatives of the Utah State Fraternal Order of Police Thursday, a discussion she said was productive.

Now-retired Unified Deputy Police Chief Chris Bertram agreed that police often cause problems at protests but said they must strike a careful balance, being sure to take action against those who try to harm others or damage public buildings. He questioned whether investigators focused on gangs had time to do so amid near-daily demonstrations in recent months.

He believes officers across the country are hesitating to intervene in instances they typically would have in the past, thinking, “I‘m going to avoid those situations, because the person may not be engaged in criminal activity, and all of a sudden, I got a complaint or something turned south and I have to use force. And then I’m scrutinized and I may be losing my job or people are protesting my house in my family,” Bertram said. “I get paid the same salary if I just respond to calls, and I don’t proactively go out and stop that person on the corner that I believe may be dealing drugs and may have a weapon on them.”