The murder has shocked the nation and prompted calls for a review of security measures for lawmakers carrying out constituency work.
Amess, 69 and a member of Prime Minister Boris Johnson’s ruling Conservative Party, died after being stabbed several times at around midday Friday at Belfairs Methodist Church in Leigh-on-Sea, England.
A 25-year-old man was arrested on suspicion of murder and a knife was recovered, police said. He is believed to have acted alone.
“The early investigation has revealed a potential motivation linked to Islamist extremism,” the Metropolitan Police said in a statement overnight. Two addresses in the London area are being searched, the force said.
The man arrested is believed to be a British national with Somali heritage, official sources have told UK news agency PA Media. The UK’s Counter Terrorism Command is leading the investigation into the killing, police said Friday.
A somber-looking Johnson carried a wreath of pale roses Saturday morning to leave in front of the church where Amess was attacked.
He and Starmer were accompanied by Home Secretary Priti Patel, whose government department is responsible for policing and counter-terrorism efforts in the UK. Chief Constable of Essex Police Ben-Julian Harrington and other dignitaries also carried flowers to the scene.
Patel tweeted Friday that questions were “being rightly asked” about the safety of lawmakers, adding she “will provide updates in due course.”
MPs in Britain typically meet with residents in their constituencies face to face during “surgeries,” and it is uncommon for them to have a security detail.
“Until the Home Secretary’s review of MP security is complete I would recommend a temporary PAUSE in face to face meetings,” he said.
Johnson: ‘We lost a fine public servant’
The country’s political, religious and societal leaders, and its royal family, all condemned the attack and paid tribute to Amess.
Those who knew him described Amess — who was married with five children — as a dedicated local representative, deeply embedded within his community and uninterested in the careerism of national politics.
Amess entered Parliament in 1983, initially representing the Basildon constituency, and had served continuously in the House of Commons since then, making him one of the longest-serving lawmakers in the chamber.
Lawmakers from across the political spectrum spoke Friday of their sadness, concern, and anger that another of their colleagues was killed while meeting with constituents.
In a statement Friday from Downing Street, Johnson said the MP “was one of the kindest, nicest, most gentle people in politics.”
“David was a man who believed passionately in this country and in its future,” Johnson said. “We lost today a fine public servant.”
Opposition leader Starmer wrote on Twitter: “Horrific and deeply shocking news. Thinking of David, his family and his staff.”
Former Prime Minister David Cameron said Amess was “a kind and thoroughly decent man” and “the most committed MP you could ever hope to meet.”
“Words cannot adequately express the horror of what has happened today. Right now, my heart goes out to David’s family,” Cameron said. Cameron’s successor Theresa May added the news was “heartbreaking” and “a tragic day for our democracy.”
And former Labour leader Tony Blair said in a statement to PA Media: “David and I came into Parliament together in 1983. Though on opposite political sides I always found him a courteous, decent and thoroughly likeable colleague who was respected across the House.
“This is a terrible and sad day for our democracy,” Blair said.
Flags outside Parliament were lowered to half staff after Amess’ death.
Amess was knighted in 2015 for his political service. He supported Britain’s departure from the European Union, and his main areas of expertise were animal welfare and pro-life issues, according to a biography on his website.
He was not considered a controversial politician, and despite the length of his tenure, he was not a widely known political figure in the UK.
In a book he wrote last year about being an MP, Amess said Cox’s murder was “totally unexpected” and the event had changed the way MPs interact with members of the public, particularly in relation to constituency surgeries.
“These increasing attacks have rather spoilt the great British tradition of the people openly meeting their elected politicians,” he wrote. “I myself have over the years experienced nuisance from the odd member of the general public at my own property. We regularly check our locks.”
CNN’s Nada Bashir and Nic Robertson reported from Leigh-on-Sea and Laura Smith-Spark wrote from London. CNN’s Sharon Braithwaite and Rob Picheta contributed to this report.