Meanwhile, Federal prosecutors have offered an ominous new assessment of last week's siege of the US Capitol, saying that rioters intended "to capture and assassinate elected officials."
The FBI is investigating 37 people in the killing of Brian Sicknick, a police officer who died a day after physically engaging with a mob of supporters of President Donald Trump who stormed the US Capitol last week, the New York Times has reported.
The FBI detailed its investigation in a memo sent to the private sector and others on Friday, the newspaper reported.
As rioters overpowered Capitol police, Sicknick was pepper-sprayed and hit in the head, his father told Reuters last week.
Ambulance crews resuscitated him twice as he was rushed to a nearby Washington hospital. Sicknick died the next day.
The FBI did not immediately respond to a request for comment.
Sicknick’s death is being investigated as a homicide by the Washington Metropolitan Police. The FBI is assisting.
Sicknick was the fifth person to die after Trump supporters rioted at the US Capitol on Wednesday.
The Republican president had summoned them to Washington for a rally and urged them to fight as lawmakers were meeting to certify his November election loss to Democrat Joe Biden.
The deaths included some rioters.
Fourteen other Capitol Police officers were injured in the riot, the FBI memo said, according to the New York Times.
Ominous new assessment
Federal prosecutors offered an ominous new assessment of last week's siege of the US Capitol by President Donald Trump's supporters, saying in a court filing that rioters intended "to capture and assassinate elected officials."
Prosecutors offered that view in a filing asking a judge to detain Jacob Chansley, the Arizona man and QAnon conspiracy theorist who was famously photographed wearing horns as he stood at the desk of Vice President Mike Pence in the chamber of the US Senate.
The detention memo, written by Justice Department lawyers in Arizona, goes into greater detail about the FBI's investigation into Chansley, revealing that he left a note for Pence warning that "it's only a matter of time, justice is coming."
"Strong evidence, including Chansley's own words and actions at the Capitol, supports that the intent of the Capitol rioters was to capture and assassinate elected officials in the United States government," prosecutors wrote.
A public defender representing Chansley could not be immediately reached for comment. Chansley is due to appear in federal court on Friday.
The prosecutors' assessment comes as prosecutors and federal agents have begun bringing more serious charges tied to violence at the Capitol, including revealing cases on Thursday against one man, retired firefighter Robert Sanford, on charges that he hurled a fire extinguisher at the head of one police officer and another, Peter Stager, of beating a different officer with a pole bearing an American flag.
'Attempt to violently overthrow the US government'
In Chansley's case, prosecutors said the charges "involve active participation in an insurrection attempting to violently overthrow the United States government," and warned that "the insurrection is still in progress" as law enforcement prepares for more demonstrations in Washington and state capitals.
They also suggested he suffers from drug abuse and mental illness, and told the judge he poses a serious flight risk.
"Chansley has spoken openly about his belief that he is an alien, a higher being, and he is here on Earth to ascend to another reality," they wrote.
The Justice Department has brought more than 80 criminal cases in connection with the violent riots at the US Capitol last week, in which Trump's supporters stormed the building, ransacked offices and in some cases, attacked police.
Many of the people charged so far were easily tracked down by the FBI, which has more than 200 suspects, thanks in large part to videos and photos posted on social media.
Michael Sherwin, the Acting US Attorney for the District of Columbia, has said that while many of the initial charges may seem minor, he expects much more serious charges to be filed as the Justice Department continues its investigation.
Capitol rioters included highly trained ex-military, cops
As President Trump’s supporters massed outside the Capitol last week and sang the national anthem, a line of men wearing olive-drab helmets and body armour trudged purposefully up the marble stairs in a single-file line, each man holding the jacket collar of the one ahead.
The formation, known as “Ranger File,” is standard operating procedure for a combat team that is “stacking up” to breach a building — instantly recognisable to any US soldier or Marine who served in Iraq and Afghanistan. It was a chilling sign that many at the vanguard of the mob that stormed the seat of American democracy either had military training or were trained by those who did.
An Associated Press review of public records, social media posts and videos shows at least 21 current or former members of the US military or law enforcement have been identified as being at or near the Capitol riot, with more than a dozen others under investigation but not yet named. In many cases, those who stormed the Capitol appeared to employ tactics, body armour and technology such as two-way radio headsets that were similar to those of the very police they were confronting.
Experts in homegrown extremism have warned for years about efforts by far-right militants and white-supremacist groups to radicalise and recruit people with military and law enforcement training, and they say the January 6 insurrection that left five people dead saw some of their worst fears realised.
“ISIS [Daesh] and Al Qaeda would drool over having someone with the training and experience of a US military officer,” said Michael German, a former FBI agent and fellow with the Brennan Center for Justice at New York University. “These people have training and capabilities that far exceed what any foreign terrorist group can do. Foreign terrorist groups don’t have any members who have badges.”
Among the most prominent to emerge is a retired Air Force lieutenant colonel and decorated combat veteran from Texas who was arrested after he was photographed wearing a helmet and body armour on the floor of the Senate, holding a pair of zip-tie handcuffs.
Another Air Force veteran from San Diego was shot and killed by a Capitol Police officer as she tried to leap through a barricade near the House chamber. A retired Navy SEAL, among the most elite special warfare operators in the military, posted a Facebook video about traveling from his Ohio home to the rally and seemingly approving of the invasion of "our building, our house.”
Two police officers from a small Virginia town, both of them former infantrymen, were arrested by the FBI after posting a selfie of themselves inside the Capitol, one flashing his middle finger at the camera.
Also under scrutiny is an active-duty psychological warfare captain from North Carolina who organised three busloads of people who headed to Washington for the “Save America” rally in support the president’s false claim that the November election was stolen from him.
While the Pentagon declined to provide an estimate for how many other active-duty military personnel are under investigation, the military’s top leaders were concerned enough ahead of President-elect Joe Biden’s inauguration that they issued a highly unusual warning to all service members this week that the right to free speech gives no one the right to commit violence.
The chief of the US Capitol Police was forced to resign following the breach and several officers have been suspended pending the outcome of investigations into their conduct, including one who posed for a selfie with a rioter and another who was seen wearing one of Trump’s red “Make America Great Again” caps.
Over 110 arrested
More than 110 people have been arrested on charges related to the Capitol riot so far, ranging from curfew violations to serious federal felonies related to theft and weapons possession.
Brian Harrell, who served as the assistant secretary for infrastructure protection at the Department of Homeland Security until last year, said it is “obviously problematic” when “extremist bad actors” have military and law enforcement backgrounds.
“Many have specialised training, some have seen combat, and nearly all have been fed disinformation and propaganda from illegitimate sources,” Harrell said.
“They are fuelled by conspiracy theories, feel as if something is being stolen from them, and they are not interested in debate. This is a powder keg cocktail waiting to blow.”
Plans for armed protests
The FBI is warning of the potential for more bloodshed. In an internal bulletin issued on Sunday, the bureau warned of plans for armed protests at all 50 state capitals and in Washington, DC, in the coming weeks.
Meanwhile, police departments in such major cities as New York, Los Angeles, Las Vegas, Houston and Philadelphia announced they were investigating whether members of their agencies participated in the Capitol riot.
The Philadelphia area's transit authority is also investigating whether seven of its police officers who attended Trump’s rally in Washington broke any laws.
A Texas sheriff announced last week that he had reported one of his lieutenants to the FBI after she posted photos of herself on social media with a crowd outside the Capitol. Bexar County Sheriff Javier Salazar said Lt Roxanne Mathai, a 46-year-old jailer, had the right to attend the rally but he’s investigating whether she may have broken the law.
One of the posts Mathai shared was a photo that appeared to be taken January 6 from among the mass of Trump supporters outside the Capitol, captioned: “Not gonna lie. ... aside from my kids, this was, indeed, the best day of my life. And it’s not over yet.”
A lawyer for Mathai, a mother and longtime San Antonio resident, said she attended the Trump rally but never entered the Capitol.
In Houston, Police Chief Art Acevedo said an 18-year veteran of the department suspected of joining the mob that breached the Capitol was placed on leave and will face a disciplinary hearing.
“There is no excuse for criminal activity, especially from a police officer,” Acevedo said. “I can’t tell you the anger I feel at the thought of a police officer, and other police officers, thinking they get to storm the Capitol.”