LONDON - The lone attacker who carried out a deadly rampage in central London was a British-born man once investigated for possible extremist links, but was "not part of the current intelligence picture," Britain's prime minister said Thursday.
The remarks by Theresa May did not name the suspect who left three people dead - two mowed down by his SUV on the Westminster Bridge and a police officer stabbed outside Parliament - before he was fatally shot.
But May offered new details about his past scrutiny by authorities, who described Wednesday's attacks as "inspired by international terrorism" but likely waged by the suspect alone.
In a statement to the House of Commons, May said that the assailant was born in Britain and was once investigated by security services " in relations to concerns about violent extremism"
"He was a peripheral figure," she added. "The case was historic. He was not part of the current intelligence picture. There was no prior intelligence of his intent or of the plot. Intensive investigations continue"
Meanwhile, police held at least eight people in sweeps in London and Birmingham linked to the investigation.
Mark Rowley, the acting deputy police commissioner, said: "It is still our belief, which continues to be borne out by our investigation, that this attacker acted alone and was inspired by international terrorism."
Speaking outside the Scotland Yard headquarters, Rowley said that four people had died, including two members of the public, a police officer, and the attacker. On Thursday, the police said that five people had died, but have since revised down that figure.
He also said that 29 people were being treated in hospital, with seven in critical condition.
"At this stage, we have no specific information about further threats to the public," he said.
A minute's silence was observed in Parliament, Scotland Yard and London's City Hall to honor the lives lost in the attack at 9:33 a.m., in honor of slain police officer Keith Palmer's shoulder number 933 on his uniform.
Queen Elizabeth II, who was due to open the new Scotland Yard building today but postponed it in light of events, said that her "thoughts, prayers, and deepest sympathy are with all those who have been affected by yesterday's awful violence."
On Wednesday afternoon, an assailant plowed an SUV through terrified pedestrians along a landmark bridge, killing at least two people and injuring others from a range of nationalities, including 12 Britons, three French schoolchildren, two Romanians, four South Koreans, two Greeks, one German, one Pole, one Irish, one Chinese, one Italian, and one American.
One woman who was walking along Westminster Bridge fell into the Thames, but was pulled alive from the river.
He then rammed the vehicle into the fence encircling Parliament and charged with a knife at officers stationed at the iron gates leading to the Parliament grounds, killing one and injuring three, before he was shot and killed by police. Tributes have been pouring in for Palmer, a 48-year-old husband and father who was unarmed at the time of the attack.
"He was a strong, professional public servant," said the lawmaker James Cleverly in emotional speech in Parliament.
Lawmakers also acknowledged Tobias Ellwood, a senior official at Foreign Office Minister who tried in vain to save Palmer's life.
Michael Fallon, Britain's Defence Secretary, said that the security arrangements at Parliament, which has a mix of armed and unarmed officers, would now be reviewed. But he stressed that that "Parliament cannot be hermetically sealed."
The incident was splashed onto the front pages of British newspapers on Thursday with the Times of London carrying the headline "Assault on Westminster" and the Daily Mirror "Attack on Democracy."
Despite the massive police presence in the area, there were signs that life was returning to normal on Thursday.
"We are not afraid," May said during her defiant speech to Parliament, which was busier than normal.
The attack occurred on Parliament's busiest day of the week, when the prime minister appears for her weekly questions session and the House of Commons is packed with visitors.
The Palace of Westminster, the ancient seat of the British Parliament, is surrounded by heavy security, with high walls, armed officers and metal detectors. But just outside the compound are busy roads packed with cars and pedestrians.
The attack - a low-tech, high-profile assault on the most potent symbol of British democracy - fits the profile of earlier strikes in major European capitals that have raised threat levels across the continent in recent years.
It was apparently carried out by a lone assailant who used easily available weapons to attack and kill people in a busy public setting.
British security officials have taken pride in their record of disrupting such attacks even as assailants in continental Europe have slipped through. On Thursday, May said that since June 2013, police and intelligence services have disrupted 13 terrorist plots in Britain.
But they have also acknowledged that their track record would not stay pristine, and that an attack was inevitable. When it happened, it was shocking nonetheless. Cellphones captured scenes of carnage amid some of London's most renowned landmarks.
The target - Westminster - was heavily guarded. But the weapons of choice - an SUV and a knife - made the attack one of the most difficult kinds to prevent, requiring the assailant neither to acquire illegal weapons nor to plot with other conspirators.
Britain has been on high alert for terrorist attacks for several years. But until Wednesday, the country had been spared the sort of mass-casualty attacks that have afflicted France, Belgium and Germany since 2015.
A year ago to the day, attackers carried out three coordinated suicide bombings in Belgium, killing 32 civilians and injuring more than 300 others in two blasts at Brussels Airport and one at a metro station in the Belgian capital. The Islamic State asserted responsibility for the attacks, in which three perpetrators were also killed.
Specialists said the attack appeared to be in line with an emerging model of strikes involving simple, everyday instruments but carried out in locations sure to draw global attention.
"Terrorists rely on a lot of people watching - it can be even better than having a lot of people dead," said Frank Foley, a scholar of terrorism and counterterrorism at the Department of War Studies at King's College London.