The FBI has investigated local police departments it believes may have been infiltrated by white supremacist groups, according to a counterterrorism policy guide.
"Domestic terrorism investigations focused on militia extremists, white supremacist extremists, and sovereign citizen extremists often have identified active links to law enforcement officers," reads the 2015 guide obtained by The Intercept.
But concerns over white supremacist infiltration into local police departments isn't new.
In 2006, an FBI internal intelligence assessment said there was evidence that white supremacist groups have "historical" interest in "infiltrating law enforcement communities or recruiting law enforcement personnel."
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Such infiltration "can lead to investigative breaches and can jeopardize the safety of law enforcement sources or personnel," according to the memo.
The memo also expressed concern about "ghost skins," a term used among white supremacists to describe "those who avoid overt displays of their beliefs to blend into society and covertly advance white supremacist causes."
One case referred to a white supremacist group that encouraged ghost skins to work in law enforcement to get information about any potential investigations.
White supremacist groups working in law enforcement is not a newly discovered phenomenon.
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The roots of white supremacy in policing can be traced all the way back to the days of slavery, according to Eastern Kentucky University professor Victor Kappeler.
But in recent years, there has been several documented cases of white supremacists working in law enforcement, reported Fusion.
One such case was in 1991, when Los Angeles County sheriff's deputies were found to have used "terrorist-type tactics" to violate the civil rights of blacks and Latinos, according to the Los Angeles Times.
"The actions of many deputies working in the Lynwood substation are motivated by racial hostility," U.S. District Judge Terry J. Hatter Jr. wrote at the time. "These deputies regularly disregard the civil rights of individuals they have sworn to protect. Many of the incidents which brought about this motion involved a group of Lynwood-area deputies who are members of a neo-Nazi, white supremacist gang -- the Vikings -- which exists with the knowledge of departmental policy makers."