The U.S. Department of Justice sharply rebuked the Seattle Police Department today, claiming cops use excessive force that's unconstitutional 20% of the time.

During a press conference Friday, federal officials said the agency's pattern of excessive force is "systemic," a ruling expected to bring about changed in training protocols. The agency will likely agree to implement changes formalized in a consent decree.

The ruling was less severe than Thursday's accusation that the Maricopa County (Ariz.) Sheriff's Office engages in discriminatory policing.

"Our investigation has revealed that inadequate systems of supervision and oversight have permitted systemic use of force violations to persist at the Seattle Police Department," said Thomas E. Perez, assistant attorney general for the civil rights division. "The problems within SPD have been present for many years and will take time to fix."

The DOJ also found that Seattle Police officers are too quick to use impact weapons, such as batons and flashlights. When Seattle officers use batons, 57 percent of the time it is either unnecessary or excessive, according the the report.

The DOJ also claims Seattle officers escalate situations and use excessive force when arresting individuals for minor offenses, a trend that's pronounced during encounters with subjects who are mentally ill or under the influence of alcohol or drugs. The department estimates that 70% of use-of-force encounters involve these groups.

The DOJ, which analyzed use-of-force reports from Jan. 1, 2009, to April 4, 2011, noted several "entrenched deficiencies" that resulted in unlawful or troubling conduct by officers:

• Deficiencies in oversight, policies and training with regard to when and how to use force, reporting uses of force, and using impact weapons, such as batons and flashlights.

• Failure of supervisors to provide oversight of the use of force by individual officers, including appropriate investigation and review of uses of force. Among the approximately 1,230 use of force reports from January 2009 to April 2011, only five were referred for "further review."

• Ineffective systems of complaint investigation and adjudication.

• An ineffective early intervention system and disciplinary system.

• Inadequate policies and training with regard to pedestrian stops and biased policing.

• Failure to collect adequate data to assess biased policing allegations.

The DOJ has been investigating the department since March 31. The probe was launched following the deadly shooting of a homeless Native American woodcarver and other incidents of force used against minority suspects. The probe was requested by the American Civil Liberties Union of Washington .