DULUTH — An undercover officer will not face criminal charges after fatally shooting a man who ran at members of the Lake Superior violent offender task force of the Duluth Police with a tactical knife.

Zachary James Shogren, 34, died of his gunshot wounds on Feb. 24. There is no basis for charges against officers, according to the Cook County Attorney's Office, which was asked by the St. Louis County Attorney's Office to review the case to avoid perceptions of bias.

"The evidence is sufficient to establish that an objectively reasonable officer in their position would believe there was a threat of death or great bodily harm to another law enforcement officer," according a news release issued Monday from the St. Louis County Attorney's Office.

Officers at the scene were not identified because they work undercover.

Over nearly two weeks, Shogren made several "graphic and violent" threats against his family that were reported to the police. Members of the department's undercover task force approached him in an alley near his home in Duluth's Endion neighborhood.

The task force members identified themselves as police officers and asked Shogren to put his hands up. Instead he pulled a knife from his pocket and approached the officers. After a warning, Shogren was hit by an officer's Taser — but was unaffected. Another officer hit Shogren with four less-lethal rounds, which also failed to stop him.

As Shogren moved in on one of the officers, "holding the knife in a pre-strike position," another officer fired his gun twice.

Task force members provided medical assistance until an ambulance arrived. Shogren, who served in the Army National Guard and was deployed to Iraq in 2011-2012, was declared dead at the hospital.

The Minnesota Bureau of Criminal Apprehension first investigated the case before handing it off to the Cook County Attorney's Office in May. Evidence included body and dashboard camera footage and police and medical examiner reports.