By Mark Landler, Megan Specia and Stephen Castle

LONDON — As Prime Minister Boris Johnson and other British leaders paid their respects Saturday (16) to a Conservative lawmaker fatally stabbed a day earlier, the police were searching three addresses in the London area while continuing to question the 25-year-old man arrested after the attack.

Late Saturday, London’s Metropolitan Police said they had been granted a warrant under the Terrorism Act to keep the suspect in detention for six extra days in connection with the killing of David Amess in a seaside town east of London.

The police have formally declared the attack a terrorist episode, with a potential link to Islamist extremism. They have not yet publicly named the suspect, who was arrested at the scene, but the BBC, citing government sources, identified him as Ali Harbi Ali, a British national believed to be of Somali heritage.

The BBC also reported that the suspect had briefly been referred to Britain’s Prevent program, which is intended to keep people from being radicalized.

The police said in a statement that they had conducted three searches in the London area, one of which concluded Saturday, and they appealed to the public to come forward with any information that might help the investigation.

The brutal attack on Amess, at midday and in full view of the public, has stunned the British political establishment and fanned questions about the security of members of Parliament. A sombre Johnson — joined by opposition leader Keir Starmer and other officials — laid flowers outside the Methodist church in Leigh-on-Sea, a sleepy seaside community that was convulsed Friday when the lawmaker was assaulted during a routine meeting with constituents.

Lawmakers regularly meet their constituents, unprotected, to hear their concerns and grievances in sessions — known as surgeries — that can at times become heated.

An attack outside such a session in 2016 killed Jo Cox, a Labour Member of Parliament. Another, in 2010, left Stephen Timms, also a Labour lawmaker, seriously wounded after he was stabbed in the abdomen.

The stabbing of Amess has also rekindled memories of other attacks by radicalized individuals, most recently in February 2020, when a 20-year-old man with a history of extremism was shot and killed by the police after stabbing two pedestrians in South London. He was being tailed by undercover police, who interrupted the daylight assault on a busy street.

That man, Sudesh Amman, had just been released halfway into a three-year sentence on charges of distributing extremist material and possessing material that could be useful for preparing a terrorist attack.

In November 2019, the police shot and killed Usman Khan, 28, on London Bridge after he set off on a frenzied stabbing spree, killing two people and wounding three. Khan, the British-born son of Pakistani immigrants, had earlier been convicted of being part of a group that plotted to bomb London’s stock exchange.

In April, the Johnson government tightened terrorism laws, mandating that those convicted of serious acts of terrorism serve a minimum of 14 years in prison, under stricter supervision. Some legal critics argue that prolonging prison terms only serves to radicalize offenders even further.

As Scotland Yard scrambled for answers Saturday, public officials paid tribute to Amess’ long record of government service.

Commissioner Roger Hirst of the Essex Police, which has jurisdiction over Leigh-on-Sea, said in a statement that it was “a sombre moment of reflection to remember a man who worked so hard for his community, who served those he represented passionately and made a real difference for Southend.”

“As we try and come to terms with these tragic events, it is important we remember the man he was and contribution he made,” Hirst said.

On the town’s normally tranquil streets, the sudden spasm of violence had not yet fully sunk in. On Saturday morning, the police canvassed residents near the church, seeking witnesses. Chaplains consoled a steady stream of people who visited the area where Amess was killed.

Alan Dear, 76, a local councillor, spoke tearfully of the lawmaker, who he said had helped him in his own campaign for local office.

“He was just a fantastic person, very kind, loving, gentle man,” Dear said. “He spent his whole life — 40 years looking after people. All he really wanted was to solve people’s problems.”

More than just an attack on a friend, Dear said the stabbing had struck at one of the pillars of political life in Britain.

“It was an attack on David, but it was also an attack on democracy in this country,” he said. “It’s very important that we keep in contact with our constituents.”

Dear said lawmakers should be offered better protection, but not at the cost of those connections with voters. Either way, the attack kicked off an urgent debate over whether current measures are inadequate.

Stuart Andrew, the deputy chief whip in the House of Commons, said that while the events of the past day had made him feel “anxious, naturally,” he was determined not to let that deter him and would hold his open constituency meeting Saturday in honour of Amess.

The home secretary, Priti Patel, asked the police to review security and to contact each lawmaker. Speaking near the scene of the attack, Patel said that “we cannot be cowed by any individual or any motivation or people with motives to stop us from functioning to serve our elected democracy.”

Friends of Amess said he was known for his passionate campaigning on behalf of animal rights, as well as for his social conservatism. He supported a ban on fox hunting, a position that put him at odds with some fellow Conservatives, and sponsored legislation outlawing the cruel tethering of horses.

Amess was also a vocal supporter of the Iranian opposition group Mujahedeen Khalq, or MEK, which campaigns for the overthrow of Iran’s government. The group has attracted a bipartisan list of American backers, including John Bolton, who served as a national security adviser to President Donald Trump, and Howard Dean, a onetime chair of the Democratic Party.

There was no evidence linking the attack to Amess’ support for the MEK. Although the group was once designated as a terrorist organization by the United States, Britain and the European Union, all three removed that designation several years ago.

David Jones, a Conservative member of Parliament and a leader of the British Committee for Iran Freedom, which backs the MEK, hailed Amess as “a champion of human rights and democracy in Iran for more than three decades.”

-New York Times