(NewsNation) — NewsNation has learned exclusively that a man on the radar of both the FBI and D.C. police made concerning visits last week to the FBI headquarters and the Department of Justice

According to an intelligence bulletin obtained by NewsNation, the man — who at this point hasn’t been accused of a crime — was turned away from the federal buildings after he visited to “air his grievances.”

It goes on to say he shared with his mother that “he was going to find explosives and blow up an undisclosed sheriff’s office.” 

Officers have been told to look out for the man who, police say, may have mental health concerns.

This latest warning comes as federal law enforcement are on high alert after the FBI found and took away boxes of documents — some marked top secret and others classified — from former President Trump’s Florida home.

The FBI and Department of Homeland Security confirmed sending a memo out Friday regarding the heightened threat environment.

Mupltiple media outlets report that the memo warned, among other things, of a threat to place a dirty bomb outside FBI headquarters.

Also Friday, NewsNation obtained a similar memo citing online chatter from far-right extremists that “a civil war was imminent.” 

The magistrate judge who approved the Mar-a-Lago search warrant and other FBI officials have faced antisemitic threats and calls for their deaths in far-right corners of the internet.

“A pretty, pretty big uptick in that really specific set of conversations or chatter” indicates “the likelihood of some sort of heightened kind of threat situation,” Jon Lewis, who studies homegrown extremism at George Washington University, said Monday.

Lewis tells NewsNation the clearest risk from these threats is lone-wolf attacks like the one last week on the Cincinnati FBI field office.

“It’s really that lone actor, right? It’s the individual who doesn’t need to have a group affiliation or membership in some anti-government or white supremacist group. It could just be someone who is extremely online — someone who is taking in the rhetoric who, you know, is sitting at home,” Lewis said.

Yet another example of the repercussions of such rhetoric came Monday: New federal charges were unsealed against a Pennsylvania man. Prosecutors say Adam Bies of western Pennsylvania made threats on the social media site Gab, including threats to take the lives of FBI agents.