(CNN) -- The Chicago Police Department has unconstitutionally engaged in a pattern of excessive and deadly force, US Attorney General Loretta Lynch said Friday, wrapping up a 13-month federal probe of a department that has been under heavy scrutiny over officer-involved shootings.

As a result of the probe, the city and the Justice Department, which began investigating the CPD in December 2015, have agreed to negotiate a reform plan that would be overseen by a federal judge, Lynch said in Chicago.

Chicago police officers' use of excessive force, she said, stemmed in large part from what the Justice Department found were severely insufficient training and accountability procedures -- including failing to train officers to de-escalate situations.

"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," Lynch said.

"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."

Friday's announcement comes more than two years after the fatal shooting by Chicago police of 17-year-old Laquan McDonald, a case that spurred protests and reforms and helped fuel a national conversation about police officers' use of deadly force.

Shooting at fleeing suspects

In a 161-page report released Friday, the Justice Department said Chicago police officers:

• Shot at fleeing suspects who presented no immediate threat

• Shot at vehicles without justification

• Used less-lethal force, including Tasers, against people who posed no threat

• Used force to retaliate against and punish people

• Used excessive force against juveniles

-- Developing story - more to come

The-CNN-Wire
™ & © 2017 Cable News Network, Inc., a Time Warner Company. All rights reserved.