CHICAGO (AP) — The Chicago Police Department has violated the constitutional rights of residents for years, permitting racial bias against blacks, using excessive force and killing people who did not pose threats, the Justice Department announced Friday after a yearlong investigation.

Among other findings, the report concluded that the pattern was "largely attributable to systemic deficiencies" within the department and the city. It also cited insufficient training and a failure to hold bad officers accountable.

"The resulting deficit in trust and accountability is not just bad for residents — it's also bad for dedicated police officers trying to do their jobs safely and effectively," Attorney General Loretta Lynch said. The report lays "the groundwork for the difficult but necessary work of building a stronger, safer, and more united Chicago for all who call it home."

The Justice Department began investigating the nation's third-largest police force in December 2015 after the release of dashcam video showing a white police officer shoot a black teenager named Laquan McDonald, who was shot 16 times as he walked away holding a small folded knife. The video of the 2014 shooting, which the city fought to keep from being released, inspired large protests and cost the city's police commissioner his job.

Under President Barack Obama, the Justice Department has conducted 25 civil rights investigations of police departments, including Cleveland, Baltimore and Seattle. The release of a report is one step in a long process that, in recent years, has typically led to talks between the Justice Department and a city, followed by an agreed upon reform plan that's enforceable by a federal judge.

Chicago's report comes just days before a change in administration, from a White House that strongly backed the process to President-elect Donald Trump's, whose commitment to federal review is unclear.

The perception that Chicago Mayor Rahm Emanuel badly mishandled the McDonald shooting hurt the former Obama chief of staff politically, and he may feel pressure to address many of the Justice Department's findings to restore his political fortunes.

The Chicago department, with 12,000 officers, has long had a reputation for brutality, particularly in minority communities. The most notorious example was Jon Burge, a commander of a detective unit on the South Side. Burge and his men beat, suffocated and used electric shock for decades starting in the 1970s to get black men to confess to crimes they did not commit.

The McDonald video, which showed officer Jason Van Dyke continuing to shoot the teen even after he slumped to the ground, provoked widespread outrage. It was not until the day the video was released, which was more than a year after the shooting, that Van Dyke was charged with murder. He has pleaded not guilty. Police reports of the shooting later suggested a possible cover-up by other officers who were at the scene.