The Chicago Police Department is stuck in the Stone Age — from training that relies on 35-year-old videos to outdated pursuit tactics that imperil suspects, officers and innocent bystanders, according to a scathing 161-page report just released by the Justice Department.

U.S. Attorney General Loretta Lynch called for sweeping changes in a department she said engages in a “pattern or practice of use of excessive force.”

“In Chicago and around the country, reform cannot and will not happen overnight,” Vanita Gupta, head of the department’s Civil Rights Division, said at a Friday news conference alongside Lynch; Mayor Rahm Emanuel; Zachary Fardon, the U.S. attorney in Chicago; and Chicago Police Supt. Eddie Johnson.

The city and Justice Department have signed an agreement to negotiate on the proposed reforms. They say that could lead to a binding consent decree enforced in federal court. But Sen. Jeff Sessions, R-Ala., who is nominated to succeed Lynch as attorney general under President-elect Donald Trump, has expressed skepticism about such decrees.

Emanuel promised to carry out the reforms, either way.

The report describes a department in desperate need of them.

Federal investigators say they had fanned out across Chicago, speaking to everyone from cops to clergy. They say they found role models such as a Chicago Police commander who is close to the community groups in his district and even passes out his private-cell phone number to residents.

“CPD has the officers to make community policing work,” the report said.

But most of the report is a searing indictment of the Chicago Police Department — offering narratives of rookies who can’t answer basic questions about the use of force, veteran cops shooting people who don’t pose a threat, and supervisors who’d rather be friends with their officers than discipline them for using racial slurs or other misconduct.

The report takes aim at a series of “unsound tactics” that cops have used for decades to pressure or pursue suspects. The report argues that those tactics — used on the street though they’re not official department policies — can alienate communities and, in many cases, lead to unnecessary violence.

At the top of the list: foot chases. The feds found police routinely chased people simply because they’d run away and not because they were suspected of a particular crime. On many occasions, the result was a deadly shooting.

Foot pursuits are “inherently dangerous,” the report states, because they can make police tired and full of adrenaline, impairing their ability to make sound decisions. The police department “does not have a foot pursuit policy,” the report says. “It should.”

The feds were deeply critical of what’s known as a “jump out” — when cops in unmarked cars speed up to corners where people are gathered, come to an abrupt stop and hop out, ready to pursue anyone.

“In one case, a tactical officer in plain clothes jumped out of an unmarked car, chased a man who ran from him, and ultimately shot the man from behind,” the report states. “Officers claimed the man pointed a gun, but no weapon was recovered. The shooting victim explained to investigators that he ran because a sedan he did not recognize had raced through a stop sign and headed toward him.”

Last year, officers shot 27 people through mid-December. Criminals, meanwhile, shot more than 4,300 people in 2016. Last week, former police Supt. Garry McCarthy pointed out the stark difference in an interview with the Chicago Sun-Times.

“Nobody is talking about what percentage of the African-American community is victimized by crime. What we are talking about is victimization by police. The priorities are wrong,” he said.

But the feds say tactics that lead to questionable police shootings also lead to distrust of the police, which snowballs into a lack of cooperation, one reason for Chicago’s dismal 29 percent rate in solving murders last year. And that lack of certainty in getting caught emboldens criminals, the feds say.

Federal investigators heard stories of other tactics that don’t lead to police shootings, but have drawn sharp criticism from people they interviewed, such as “guns for freedom.” That’s when cops arrest people for low-level offenses and refuse to let them go until they’ve turned in illegal guns.

They also heard of cases like this:

“A young black man told us that when he was 12 or 13 years old, he and his friends were picked up by CPD officers, dropped off in rival territory, and told to walk home,” according to the report. “Another black teen told us that his brother was picked up in one location, dropped off in another location known for rival gangs, and told: ‘Better get to running.’ ”

Police have also used Tasers or threats of force to intimidate people who weren’t suspected of crimes, according to the report. One on-duty officer tracked down a group of boys who’d reportedly been playing basketball on his property.

“The officer pointed his gun at them, used profanity, and threatened to put their heads through a wall and to blow up their homes,” the report states.

The officer was suspended for five days.

In their official accounts of these incidents, officers don’t have to provide a narrative of why they used non-lethal force, the report says. And the Independent Police Review Authority – the agency charged with investigating police use of force incidents – almost never looks into Taser incidents or shootings in which no one was killed. That’s even though “the difference between a hit and a no-hit shooting case may only be a matter of bad aim.”

The report found the disciplinary system for officers is ineffective and reinforces a “code of silence” among those unwilling to talk about colleagues’ misconduct. That’s nothing new: civil-rights activists and lawyers for alleged abuse victims have been saying that for years.

Justice Department investigators pointed out that 30,000 complaints have been filed against Chicago cops over the past five years, but only 2 percent of those complaints were sustained, meaning enough evidence was found to warrant discipline.

“This is a low sustained rate,” the report says.

The police department also doesn’t have a functioning system to intervene in the behavior of officers flagged for misconduct, the Justice Department found. Only 38 officers were enrolled in the department’s intervention system from 2011 to 2016, the report says. The city is trying to reform the system, but the feds warned that won’t be “fruitful” if it’s not rooted in CPD’s culture.

Justice Department investigators focused on training, too. They said they spent about 60 hours observing police training, which they found grossly outdated and poorly taught.

An instructor showed students one video on the use of deadly force that was made about 35 years ago — long before the Supreme Court rulings that currently govern cops’ use of force. The investigation found one in six rookies were able to correctly answer basic questions about the use of force.

The police department’s field-training program is hampered by major problems, investigators found. There are too few training officers and the voluntary job, with a $3,000-a-year stipend, isn’t viewed as a path to promotion and is “a highway to nowhere,” one supervisor said. Emanuel has vowed to hire more training officers.

Too few cops are trained to respond to mentally ill people, the report says, pointing to the fatal 2015 police shooting of Quintonio LeGrier, a mentally troubled college student. A female neighbor was also killed. The officer who fired the shots never received “critical-incident” training — and even sued the city complaining he wasn’t trained properly. Emanuel says 35 percent of patrol officers will have the training by the end of 2017.

Investigators found lots of examples of officers using racist language, most of which goes unpunished. Of 350 complaints about the use of the word n—-, only four were sustained.

The report did find some bright spots, however, such as cops on patrol who stopped to talk with shopkeepers and kids who seemed genuinely happy to see them; and officers who sponsored a dance and stepped in for girls whose fathers didn’t show up.

“Most of these efforts never make the news because they are part of an officer’s daily routine: watching carefully to detect wrongdoers before they can do wrong, diligently patrolling, notwithstanding the disrespect and cold stares that are too often part of the job, and risking their lives to protect complete strangers,” federal investigators wrote.

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