The Justice Department has “reasonable cause” to believe Chicago police officers use excessive force, the agency announced Friday.

Announcing the outcome of a Department of Justice (DOJ) investigation first launched in late 2015, Attorney General Loretta Lynch said there was cause to believe the Chicago Police Department “engages in a pattern or practice of using force, including deadly force, in violation of the Fourth Amendment of the Constitution.”

“The pattern or practice results from systemic deficiencies in training and accountability, including the failure to train officers in de-escalation and the failure to conduct meaningful investigations of uses of force.

"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."

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The DOJ said in a statement separate from Lynch's conference that it had signed an agreement with the city of Chicago to address problems found during the probe.

The two entities will partner to create a federal court-enforceable consent degree addressing those problems, it said, following community input.

The investigation sprang from the police shooting death of black teenager Laquan McDonald in October 2014, which was captured on video.

Officer James Van Dyke, who is white, became the first Chicago officer in more than 35 years to be charged with a first-degree murder while on duty. He faces a minimum of 20 years in prison if convicted in the death of the 17-year-old.

The DOJ said it heard from more than 1,000 community members and over 90 community organizations while investigating Chicago's police.

The agency also accompanied line officers on over 60 ride-alongs in every police district in Chicago.

Lynch said the exhaustive study would help Chicago begin the long but crucial work of repairing ties between its residents and its law enforcement.

"With this announcement, we are laying the groundwork for the difficult but necessary work of building a stronger, safer, and more united Chicago for all who call it home," she said.