Updated July 5 at 7:43 p.m.

Boston Mayor Michelle Wu and United States Attorney Rachael Rollins today at a press conference said they were surprised by the appearance of white supremacists in the city over the weekend. They said the Boston Regional Intelligence Center — or BRIC — also seemed to have had no warning of the march by 100 members of the Patriot Front, a neo-fascist group formed in the aftermath of the Charlottesville Unite the Right rally in 2017.

Wu and Rollins said that their hands were tied in how to respond to this and other neo-fascist actions because of First Amendment protections. Wu said “these groups creep right up to the edge of the boundaries of that.”

Members of the white supremacist group carried shields and stopped traffic at various intersections as members marched through downtown Boston and Copley Square. Along the way, they allegedly attacked a Black artist, Charles Murrell, whose hand was seen covered in a bandage during a Monday press conference held in response to the demonstration. Wu said the Boston Police Civil Rights Unit is investigating the claims.

“The individuals who were involved with the assault of Mr. Murrell need to be prosecuted within the fullest extent of the law,” the mayor said.

The press conference followed a law enforcement intelligence briefing at Boston Police headquarters for Black and Latino community leaders, a group that included City Councilors Ruthzee Louijuene, Julia Mejia and Tania Fernandes Anderson, as well as Segun Idowu, the city’s chief of Economic Opportunity and Inclusion.

When asked how 100 Patriot Front members were capable of sneaking into the city under the radar of BRIC and the Joint Terrorism Task Force, or JTTF, Rollins said some information that officials have cannot be made public at this time.

Reflecting on discussions held earlier with community leaders, she added, “We had a lot of pointed questions [at the briefing]. ... If this were a Black Lives Matter protest, would the response have been different than this white supremacist group?”

FBI Special Agent in Charge Joseph Bonavolonta, speaking for the JTTF, said the agency cannot legally track domestic groups such as the Patriot Front unless a particular threshold is reached.

“There has to be certain elements that are met for us to even open up an active investigation, and that is the existence of a potential federal crime, the threat or use of force or violence in conjunction with some sort of a social or political agenda,” he said.

Yet in Coeur D’Alene, Idaho, last month, the FBI played a preemptive role in the arrests of 31 Patriot Front members hiding in a van with riot gear en route to a gay Pride event. Idaho law enforcement worked in concert with the FBI to monitor the Patriot Front in the state, which resulted in the apprehension of the neo-fascist activists, according to emails obtained by the nonprofit group Property of the People via public records requests.

Asked about the difference between what happened in Boston and the preemptive arrests in Idaho, Wu said, "What we know is that in Idaho information was received ahead of time that the intent of this group was to go disrupt and possibly incite violence at a scheduled event that was taking place — a Pride event in their community. Here, we did not have intelligence ahead of time and did not, unfortunately, know that they were planning to come here and disrupt our festivities."

Robert Trestan, director of the Anti-Defamation League of New England, said it was almost certainly what’s called a “flash demonstration,” a tactic the Patriot Front uses.

“They keep it a secret,” Trestan said. “You don’t really know until they show up. So there’s certainly some lessons to be learned. If it happens again, you need to be prepared that groups like this use a tactic of not calling in advance. They show up, which means that the city and law enforcement need to be prepared for, you know, in an instant what happens when these groups show up.”

Rollins did not directly answer questions about whether law enforcement is tracking the Patriot Front and other hate groups, but did say that their operations are often covert.

“We did not know exactly what was happening prior to it starting,” she said. “And the good news is people called 911. People did reach out to law enforcement. We want to make sure that people understand that they should be reaching out to law enforcement when they see something that makes them uncomfortable. Whether it's a crime or not we can sort that out, but we want to make sure people alert us [to the presence of hate groups].”

At a different event Tuesday, Gov. Charlie Baker said that the state government is in near-constant contact with local and federal partners.

“I wouldn't think any white supremacist organization would think Massachusetts is fertile ground,” he said. “I do think there's a certain amount of, you know, playing on the other team's turf that might have something to do with it. But we take this stuff very seriously.”

This article was updated with additional details and comments.

Produced with assistance from the Public Media Journalists Association Editor Corps funded by the Corporation for Public Broadcasting, a private corporation funded by the American people.