Chicago cops routinely shot at fleeing suspects, used force to retaliate against people, failed to investigate most misconduct claims and skewed probes to favor officers, federal authorities said Friday in a report that documented years of systemic civil rights violations by the country's second largest police department.

The findings, the result of a year-long Justice Department investigation sparked by an officer's fatal shooting of a 17-year-old boy, detail a litany of abuses over the last four years, many of them shouldered disproportionately by black and Latino people in the segregated and chronically poor neighborhoods in the city's south and west.

Faced with overwhelming evidence of a department gone astray, city officials have started negotiating with federal authorities on a series of reforms that will be overseen by a judge.

The corrections will take years and millions of dollars to implement. But the biggest obstacle will be winning over a skeptical public that has lived through years of police scandals — many involving beatings, shootings and forced confessions — and is suffering through a jump in violent crime that has turned Chicago into America's murder capital. There were 762 homicides in the city last year, nearly 300 more than 2015, largely concentrated in the same neighborhoods where the abusive policing usually occurred, investigators said.

"We make these findings acutely aware that this is a time of significant challenge for Chicago residents and police officers," said Vanita Gupta, who heads the Justice Department's Division of Civil Rights, which conducted the probe. "Gun violence has spiked. Relations between police officers and residents are strained. And officer morale is suffering. But this context only heightens the importance and urgency of our findings."

The report cites myriad examples of officers firing guns and using Tasers unnecessarily, engaging in reckless shootouts and chases, beating up juveniles in petty confrontations, and being exposed in videos as lying about their misconduct. The behavior rarely ended with discipline, in large part due to a "code of silence" to protect fellow officers.

They included:

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Officers fired 45 rounds at a man who ran from them, killing him. They claimed the man fired at them, but investigators found no evidence. The shooting was ruled justified.

An officer shot a man in the buttocks, claiming she'd opened fire after he turned toward her and raised his hand at her. No weapon was found, and the shooting was deemed justified despite the contradictory location of the bullet wounds.

Officers hit a 16-year-old girl with a baton and then Tasered her after she was asked to leave the school for having a cell phone in violation of school rules.

A plainclothes officer searching for two "Hispanic" suspects handcuffed a 12-year-old Latino boy riding his bike with his father, holding him in his patrol car before releasing him.

Officers forced a woman from her car, threw her to the ground, hit and Tased her, then claimed the force was necessary because she refused to show her hands. A video later showed her putting her hands on her car before they took her down, but the use of force was still deemed reasonable.

Mayor Rahm Emanuel called the incidents in the report "sobering" and pledged to revamp the department even if the Justice Department's approach to police reform softens under Donald Trump, who takes office Jan. 20.

Emanuel has been the target of ribbing by Trump, who has made Chicago — Obama's home town — an example of the need for a nationwide crackdown on crime. The mayor said he'd work with Trump's Justice Department to make sure the reforms stick.

"I give my word to every officer and every Chicagoan that we won't quit until we get it right," Emanuel said.

It is unclear, however, how closely a Trump Justice Department will keep tabs on Chicago or any of the 15 cities with police forces already under federal consent decrees for unconstitutional policing, part of Obama's unusually aggressive approach to police reform. The list includes Baltimore, where the Justice Department reached a settlement Thursday.

The announcements in Baltimore and Chicago signal that Obama is trying to tie up loose ends before ceding power to Trump, who has said he disagrees with the federal government meddling with local forces. Trump's choice for attorney general, Sen. Jeff Sessions, who has expressed skepticism about reform efforts and the use of consent decrees.

Related: What Would Jeff Sessions Mean for the Future of Police Reform as Attorney General?

The American Civil Liberties Union of Illinois called the federal report overdue. Director Karen Sheley noted that her organization has been pointing out bad policing policies "for decades, only to see calls for reform neglected."

A consent decree, overseen by an independent monitor, is the only solution, she said.

Federal and city officials said they were working on just that.

"Our problems are longstanding, sometimes decades old, and prior efforts at reform…have not gotten the job done," said Zachary Fardon, the U.S. Attorney for the Northern District of Illinois.

The head of the local police union, Fraternal Order of Police Lodge 7 President Dean Angelo, accused federal authorities of rushing the investigation in order to finish before Trump took office. "Everyone who reads this document should be as concerned about the timeliness of this report as the FOP is," he said in a statement.

Arguably, none of this would be happening were it not for the Oct. 20, 2014 shooting of 17-year-old Laquan McDonald by Chicago Police Officer Jason Van Dyke. The city resisted releasing video of the shooting for a year, and when it finally came to light, it sparked allegations of a cover up. The video showed Van Dyke shooting McDonald 16 times, and contradicted official versions of the encounter given by officers who were there and by department brass.

Related: Police Accounts Appear to Differ With Laquan McDonald Shooting Video

The shooting was originally deemed justified. After the video's release, Van Dyke was charged with murder.

Unlike prior calls for reform, the outrage over the McDonald video pushed Chicago over the brink. Emanuel, hoping to get ahead of the issue, announced his own investigation, which accused the department of racist policing. U.S. Attorney General Loretta Lynch announced in December 2015 that the Division of Civil Rights would conduct its own probe.

On Friday, Lynch described a pattern of misconduct by officers, but also how those officers have been failed by their commanders, sending them into the streets without enough training or incentives to avoid violent confrontations.

"The systems and policies that fail ordinary citizens also fail the vast majority of Chicago police officers who risk their lives every day to serve and protect the city," Lynch said.