Black Lives Matter activists participate in the annual Martin Luther King Holiday Peace Walk and Parade on Monday in Washington, D.C. (Alex Wong/Getty Images)

A police sergeant in St. Paul, Minn., has been placed on administrative leave after he allegedly posted an inflammatory statement online, telling motorists to run over Black Lives Matter “idiots” participating in a march on Martin Luther King Jr. Day.

“Run them over,” Sgt. Jeffrey M. Rothecker allegedly wrote on Facebook, according to Fox affiliate KMSP. “Keep traffic flowing and don’t slow down for any of these idiots who try and block the street.”

The comment was spotted on Saturday by Andrew Henderson, a community activist who monitors police activity by filming authorities and posting his footage online, according to the Star Tribune.

“I was just flabbergasted,” Henderson told the newspaper. “A law enforcement officer is supposed to serve and protect the people, not incite violence against them.”

Henderson recorded himself filing an internal affairs complaint about the post, in which he named Rothecker. Henderson told the Star Tribune that he believed the Facebook account belonged to Rothecker.

The St. Paul Police Department told KMSP that an officer “has been put on administrative leave,” though the department has not publicly identified Rothecker.

But St. Paul Police Federation attorney Chris Wachtler told the Star Tribune that the union is representing Rothecker.

Police told KMSP that the Facebook account has since been “taken down,” though they haven’t said by whom.

In a statement Tuesday, the department said it is “actively investigating” the comment, which, it noted, “may have been written by a member of the SPPD and posted on Facebook.”

“The statement is offensive, disappointing, concerning and does not reflect in any way — or align with — the views, values and practices of the Saint Paul Police Department,” the statement said, adding that the department has “a long history of supporting individuals and groups who wish to express their opinions. There is no tolerance within the department for employees who insult, threaten or attempt to silence those exercising their First Amendment rights.”

It continued: “If it is determined that the comment was written by a member of the Saint Paul Police Department, swift, strong and decisive disciplinary action will be taken.”

Citing state law, the department said it could not provide “specific information on the investigation, who is involved and what consequences may result.”

The comment on Facebook — posted under a news article by a user named “J.M. Roth” — also outlined a detailed scenario for harming a street protester and mounting a subsequent defense, according to KMSP.

“Here is the deal, you continue to drive and if you hit someone make sure you call 911 to report the accident and meet the cops a block or two away and you can justify stopping further away because you feared for your safety since the past people in this group has shown a propensity towards violence,” it read, according to KMSP. “Since they are trying to block the street and/or cross where there is no crossing you should not be charged with anything. Now, these idiots could try and sue you in civil court, but remember that it will be jury trial and so most likely it will come out in your favor.”

In a statement, St. Paul Mayor Chris Coleman said he was “outraged and disgusted” by the post and directed the police department to investigate it.

“There is no room in the St. Paul Police Department for employees who threaten members of the public,” the mayor said. “If the allegation is true, we will take the strongest possible action allowed under law.”

The department’s investigation comes at a sensitive time for local Black Lives Matter protesters. In November, they were the target of violence when a man opened fire on a crowd of demonstrators outside the Minneapolis Police Department’s Fourth Precinct Station, wounding five people who sustained non-life threatening injuries.

Hours later, police raided an apartment belonging to Allen “Lance” Scarsella and arrested him. The 23-year-old faces five counts of second-degree assault with a deadly weapon and another for second-degree armed riot.

According to the criminal complaint, Scarsella, who is white, spoke derogatorily about African Americans and stored racist images on his cellphone. He allegedly filmed himself and another man as they headed to a Black Lives Matter protest dressed in camouflage and pledging to “make the fire rise” — an apparent reference to an anarchic character in the Batman movie “The Dark Knight Rises.”

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