SEATTLE (AP) -- Seattle police have engaged in excessive force that violated federal law and the Constitution, the U.S. Justice Department said Friday.

An investigation was launched last spring following the fatal shooting of a homeless, Native American woodcarver and other reported use of force used against minority suspects. The investigation was aimed at determining whether Seattle police have a "pattern or practice" of violating civil rights or discriminatory policing, and if so, what they should do to improve.

"Our findings should serve as a foundation to reform the police department and to help restore the community's confidence in fair, just and effective law enforcement. The problems within SPD have been present for many years and will take time to fix," said Thomas E. Perez, assistant attorney general for the civil rights division.

Federal investigators said they found inadequate systems of supervision and oversight, and that officers too quickly resorted to the use of weapons like batons and flashlights. And Seattle officers escalated situations and used unnecessary force when arresting people for minor offenses, according to the Justice Department.

The American Civil Liberties Union of Washington and 34 other community groups called for the inquiry after a Seattle officer shot and killed the woodcarver, John T. Williams, in 2010.

Video from Officer Ian Birk's patrol car showed Williams crossing the street holding a piece of wood and a small knife, and Birk exiting the vehicle to pursue him. Off camera, Birk quickly shouted three times for Williams to drop the knife, then fired five shots. The knife was found folded at the scene, but Birk later maintained Williams had threatened him.

Birk resigned from the force but was not charged. A review board found the shooting unjustified.

Other incidents captured on surveillance or police-cruiser video include officers using an anti-Mexican epithet and stomping on a prone Latino man who was mistakenly thought to be a robbery suspect; an officer kicking a non-resisting black youth in a convenience store; and officers tackling and kicking a black man who showed up in a police evidence room to pick up belongings after he was mistakenly released from jail.

There was no finding that the Seattle Police Department engaged in discriminatory policing, but federal investigators believe this area needs more research.

"The solution to the problems identified within the Seattle Police Department will require strong and consistent leadership along the chain of command, effective training and policies, and vigilant oversight," said Jenny A. Durkan, U.S. Attorney for the Western District of Washington, who joined Perez for Friday's announcement.

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