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A mentally ill man being held at the Minnesota Security Hospital in St. Peter killed another resident Wednesday and has been arrested, an act that has top state officials moving quickly to determine how the incident happened, authorities said Thursday.

The killing of convicted murderer Michael F. Douglas, 41, of Mankato, occurred Wednesday night. Darnell D. Whitefeather, 31, was being held in the Nicollet County jail on probable cause of murder, according to the St. Peter Police Department.

Department of Human Services Deputy Commissioner Anne Berry said in a statement that she and her agency's employees are "doing everything we can to assist" investigators. Longtime employees said this was the first homicide in the hospital in at least 30 years.

The state Bureau of Criminal Apprehension (BCA) immediately began investigating the death at the hospital, where more than 300 of the Minnesota's most dangerous and mentally ill patients are housed.

The state Health Department and the ombudsman for the mentally ill and developmentally disabled will also be involved.

In the past two years, patient-security issues at the hospital have pitted staff members against administrators, who have tried to find a balance between a lockdown mentality and greater freedom for patients to interact with one another.

Previously, patients were not allowed to go into the rooms of other patients, a rule intended to prevent assaults.

Douglas was convicted of second-degree murder in 1992 in Mankato. After completing his prison term, he was put on supervised release in April. In December, a judge committed him to the hospital, according to corrections officials.

Whitefeather, who has yet to be charged, lived at one time in Bemidji and has a violent criminal history spanning many years, according to court records. He was committed to the Security Hospital on Oct. 18, according to court records.

Assault a week ago recounted

A source with direct knowledge of the events told the Star Tribune that a week ago Whitefeather had tried to kill a resident while housed in the Competency Restoration Program, a unit where less volatile patients are treated.

Whitefeather was kept in seclusion for several hours and then moved to the 800 Unit, where the center's most dangerous patients reside.

Douglas was found bloodied and unconscious in his room shortly before 6:30 p.m. by a security counselor making hourly rounds, according to the source.

St. Peter police officers were called to the hospital, and paramedics tried in vain to revive him, according to police.

Security counselors soon found that Whitefeather had tried to clean his bloodied clothes in a washer on the unit and was locked in his room while staffers waited for police, the source said.

BCA agents took Whitefeather's wet clothing as evidence.

Whitefeather admitted in federal court in 2001 to kicking in the door of a home on the Red Lake Indian Reservation and bashing a man in the head with a metal pipe, leaving him unconscious. He also hit another man in the house with the pipe, court records show.

In a separate case, Whitefeather also admitted to robbing two Red Lake Band members of their pickup truck at knife point in February 2001, according to court records.

In January 2013, he assaulted the director of the Bemidji Community Behavioral Health Hospital. He was convicted and put on probation. Then in July, Whitefeather was charged with breaking into a Bemidji coffee shop and stealing a register with cash in it.

Security challenges

Roberta Opheim, the state ombudsman for people with mental illness and developmental disabilities, said hospital administrators will surely be asked to show what risk-assessment plans were in place to protect Whitefeather from harming himself or others.

"Every patient admitted has to have a risk-assessment plan," she said. "If he has had a previous incident [the assault a week earlier], the hospital will have to say whether they readjusted his risk plan or not. We have no knowledge yet whether they did this or not."

Staff writer David Chanen contributed to this report. 612-673-1745 612-673-4482