"I am confident that justice will be served" in the Floyd case, Attorney General William Barr said in a statement Friday, calling the video of Floyd's death "harrowing to watch and deeply disturbing."

But former DOJ attorneys said they doubt Barr would be interested in such wide-ranging cases. And even if investigations were opened, a department policy put in place by Barr's predecessor, Jeff Sessions, severely restricts prosecutors' ability to seek consent decrees, court-enforced agreements with police agencies that mandate reforms.

A DOJ spokesperson did not respond to a request for comment about the department's use of police investigations, or its plans to address the Floyd, Taylor and Arbery killings.

"It's an abdication of their responsibility," said Emily Gunston, a lawyer who helped lead several DOJ investigations of police departments during the Obama administration. Without the department training its sights on law enforcement agencies, she said, "it means that there's just no check on these police departments."

A powerful tool to fight police misconduct

Congress gave the Justice Department the power to investigate biased policing practices in 1994, in the wake of the police beating of black Los Angeles motorist Rodney King and five days of rioting in the city when four of the officers were acquitted about a year later. A new law let the DOJ open investigations and file civil lawsuits against any law enforcement agency with a "pattern or practice" of violating constitutional rights.

Those investigations typically last months or years and involve holding public meetings, interviewing officers and community members, analyzing data about the local justice system and digging into case files. Ultimately, the DOJ can file a lawsuit to put in place a court-enforced consent decree, which would require a law enforcement agency to make specific reforms and allow a federal judge to monitor their progress.

The power was used most aggressively under the Obama administration, which stepped up the use of consent decrees. Court-enforced agreements in cities like Ferguson, Cleveland and Baltimore included laundry lists of reforms departments agreed to comply with, from deescalation training and body cameras to changes in law and more equitable hiring practices.

One high-profile shooting isn't enough to justify a pattern or practice investigation, former DOJ lawyers said -- but sometimes cases that capture the national attention help cast a spotlight on more systemic defects, such as police departments' excessive use of force or racially biased policies.

"You can't look at one case in isolation," said Sharon Brett, an attorney at Harvard Law School's Criminal Justice Policy Program who worked on police investigations as a DOJ lawyer. "You'd have to show the constitutional violation occurring across more than one case."

The Minneapolis, Louisville and Glynn County, Georgia, police departments have never been the subject of pattern or practice investigations. And activists in all three jurisdictions have argued that the recent high-profile killings aren't isolated incidents but are examples of deeper-rooted problems.

One of the observations she said DOJ made was that police can do something simple to deescalate or at least prevent escalation during angry protests by simply not appearing confrontational. "If officers didn't have to be in riot gear, we put them in polos and khakis," she said. "And the city -- everyone on down, council members, everyone in leadership has to train for an event like what you are seeing today in Minneapolis." The city had begun to address that when the city's mayor demanded her resignation in 2017 after a high-profile police-involved shooting. Harteau said she doesn't know what training has happened since she left.

The Glynn County Police Department did not respond to CNN's request for comment.

Christy Lopez, a Georgetown Law professor and former DOJ lawyer who worked on police practice cases, said that she found it important to pay attention to local officials' reactions after a high-profile shooting occurred.

"If the reaction is one of shock and surprise and an immediate attempt to figure out what happened," it's an indication that the incident might be an aberration, she said. But undue delays for law enforcement action after the Arbery and Taylor shootings could suggest "there might be tolerance for similar conduct more broadly," she said.

Trump administration hits brakes on investigations

So far, the wide-ranging investigations and consent decrees that defined the Obama administration's approach to police misconduct have all but disappeared under Trump.

The document "required attorneys to jump through ridiculous hoops in order to pursue a consent decree," Yeomans said. It is essentially telling attorneys "you cannot pursue the most effective tool you have for reigning in police misconduct."

Meanwhile, the team that handled police practice cases saw numerous staff departures after Sessions made clear those investigations weren't a priority, several former lawyers who worked in the group told CNN.

"The Trump administration has intentionally stripped its own capacity to address problems in local policing," said Margo Schlanger, a University of Michigan law professor who tracks civil rights litigation. "They had all these tools... On some of them, they've cut off their own hands, on some they've tied their hands behind their back."

The president himself has also seemed to encourage police misconduct. In a 2017 speech in New York, he told uniformed officers "please don't be too nice" with suspects. "When you guys put somebody in the car and you're protecting their head, you know, the way you put their hand over?" Trump said, making a motion with his hand to imitate an officer preventing a suspect's head from hitting a squad car. "I said, you can take the hand away, okay?" His press secretary later said he was joking.

Louis Dekmar, a former president of the International Association of Chiefs of Police and a police chief in Georgia, worked as a DOJ police monitor between 2004 and 2007 making sure that a police department in his state made federally requested improvements.

Given the number of problems at the Glynn County Police Department, he thinks the DOJ should conduct a sweeping investigation of its practices.

But he also said that the DOJ went overboard in attempting to institute changes in departments it investigated during the Obama administration. The DOJ "started mandating principles and philosophy like what kind of policing an agency should be doing, what constitutes community policing," he said. "That's why you saw the frustrations you did from police unions. It was too much."

In contrast, he said, the Trump administration has given large grants to the police chiefs association to train officers, which Dekmar argued was an effective way to improve policing.

Still, activists say stronger federal oversight could help defuse some of the anger that has caused protests to devolve into violence in recent days.

When people lose confidence that police misconduct will be punished, "you have what's going on right now: citizens operating out of order because the justice system hasn't been operating in order," said Rev. John Perry, the president of the local NAACP branch in Glynn County, where Arbery was shot and killed. "Part of securing the peace is showing our citizens we're serious about accountability."

From investigating police to challenging stay-at-home orders

Even as federal police investigations have all but disappeared, the DOJ has used the same statute that allows it to crack down on rogue law enforcement agencies for another target in recent weeks: Covid-19 stay-at-home orders.

In at least two cases so far, DOJ lawyers have backed lawsuits by churches against governments that are banning them from operating under restrictions on gatherings. Bans that are unfairly applied to churchgoers and not to people conducting other essential activities violate the Constitution, the department argued, citing the same law that bans police departments from systematically singling out people of a certain race.

Virginia "cannot treat religious gatherings less favorably than other similar, secular gatherings," the DOJ wrote in its brief supporting an evangelical church that faced criminal charges after holding a service with 16 people. The department argued that the Northam's stay-home order unfairly bans "church services or other religious gatherings that exceed ten people, despite permitting various other gatherings that may result from secular activities."

Former DOJ lawyers say it's ironic that the department is suddenly using the same statute it has all but given up on for police cases.

"They are using the police misconduct statute -- for the second time in three years -- in a case where plaintiffs are not even suing the police, but rather the Democratic governor," Lopez said. "It certainly raises the question in my mind whether this is more about politics than police accountability."