An Oregon State Police detective who investigated a 2011 Northwest killing spree by a pair of white supremacists is expected to plead guilty to charges of forgery and official misconduct related to the case, a prosecutor said Wednesday.

Detective David Steele will enter the plea Friday at his arraignment in Salem and be sentenced, Marion County deputy district attorney Paige Clarkson announced in a statement.

Further details of the apparent plea agreement were not immediately available.

Steele's attorney, Mike Staropoli, declined to speak about what he described as an open and pending case.

The charges stemmed from Steele's work in the case against Joey Pedersen and Holly Grigsby, who were convicted after a nine-day rampage that claimed the lives of Pedersen's father and stepmother, an Oregon teenager the couple mistakenly thought was Jewish, and a black man in Northern California.

Steele was the lead investigator until his removal in the fall of 2013. The agency placed him on paid administrative leave last December.

U.S. District Judge Ancer Haggerty sharply criticized Steele and prosecutors in a 63-page supervisory opinion filed after Pedersen and Grigsby received life sentences earlier this year.

The judge wrote that Steele withheld and destroyed evidence, and backdated reports regarding evidence in the case. Authorities say the detective also intercepted legal mail intended for Pedersen and listened to confidential jail calls between Pedersen and his attorneys.

"The most troubling aspect of the conduct in this case is that, in large part, the government, which was aware of the problems to a substantial degree, did not alert the court of these problems of its volition," Haggerty wrote. 'It is unclear when, if ever, the government would have raised these issues."

The alleged actions were taken in what appeared to be an open-and-shut case. Grigsby and Pedersen were arrested Oct. 5, 2011, outside Yuba City, California, when a police officer spotted them in the car of one of the victims. Grigsby told officers they were on their way to Sacramento to "kill more Jews,'" court documents said. They also confessed to reporters in jailhouse interviews.

Pedersen's lawyers, Richard Wolf and Renee Manes, said it's appropriate that Steele will be prosecuted. They said defense attorneys often worry about police engaging in unethical conduct.

"Unfortunately our concerns are rarely provable and are rarely taken seriously," Manes said. "Courts tend to believe prosecutors when prosecutors tell them things under oath. But at least in our experience, the reality is that law enforcement lies."

"Regularly," added Wolf. "It's just in this case we were able to prove it and convince the court that it happened."

Pedersen gained leverage from the botched investigation, accepting a plea agreement that netted lighter sentences for a couple who helped him during the killing spree. He personally benefited from the deal by getting a grilled salmon dinner in jail.

At his August sentencing, Pedersen said police and prosecutors must be held accountable for their actions.

"We all know what to do with me, but what of them?" he told the court.

State police said in a statement Wednesday that it has been reviewing prior cases involving Steele and is "committed to learning from this situation and preventing it in the future."

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