(CNN) -- Federal civil rights investigators have found "reasonable cause" to believe that police in Portland, Oregon, use "unnecessary or unreasonable force" with persons who have mental illness, the U.S. Justice Department said.
The department's civil rights division and U.S. Attorney's Office in Oregon issued a letter to Portland Mayor Sam Adams stating that local and federal authorities will "continue our collaborative relationship to craft sustainable remedies."
In the 42-page letter, federal officials outline remedies that include training and new policies to investigate alleged police misconduct.
Investigators found cause to believe that the Portland Police Bureau engages in "a pattern or practice of using excessive force in encounters involving people with actual or perceived mental illness."
"We found instances that support a pattern of dangerous uses of force against persons who posed little or no threat and who could not, as a result of their mental illness, comply with officers' commands," said the letter, which was signed by Assistant Attorney General Thomas E. Perez and U.S. Attorney Amanda Marshall.
"We also found that PPB employs practices that escalate the use of force where there were clear earlier junctures when the force could have been avoided or minimized."
One incident in December 2010 involved several officers who used "repeated closed-fist punches and repeated shocking of a subject who was to be placed on a mental health hold," the letter said.
Adams, in a posting on his web page, vowed that the city and its Police Bureau would improve quickly, and listed a series of changes:
-- The city will revise its use-of-force policies -- particularly those regarding the use of stun guns -- "to ensure that officers have necessary guidance when encountering someone with mental illness or perceived to have mental illness."
-- The police will expand their Mobile Crisis Unit -- composed of an officer and a mental health worker -- "to ensure availability at all times and enhance non-law enforcement capacity to respond to persons in crisis that do not pose a public safety threat."
-- The city will establish a mental health desk at its 911 calling center to ensure calls are properly dispatched.
-- The city will lead efforts to boost community mental health treatment options, such as establishing a 24-hour secure drop-off and walk-in center, "that will provide police officers more options when assisting persons experiencing a mental health crisis."
-- The city will use an early intervention system to identify officers, supervisors and units "for non-punitive corrective action, and to assess gaps in policy, training, supervision and accountability."
-- The city will move to speed investigations of complaints about possible officer misconduct.
-- A community body composed of representatives of a variety of groups will assess how well the agreement is being implemented, offer recommendations on additional steps, and advise the police chief and Adams on how to improve community relations.