Conservative MP Sir David Amess died after being stabbed multiple times at his Essex constituency surgery, in what police are treating as a terrorist incident.
Here’s how the attack unfolded and what we know so far.
The MP for Southend West was stabbed at Belfairs Methodist Church in Leigh-on-Sea, in Essex. He was there for one of his regular Friday meetings with his constituents.
Just 15 minutes before the attack, the 69-year-old was standing on the church steps, chatting and laughing with locals.
At around 12:05 BST on Friday, Sir David walked into the church alongside two female members of his staff to meet some more constituents.
Local councillor John Lamb said that it was then that the attacker emerged from a small group of waiting constituents and attacked Sir David, stabbing him several times.
“I’m told that when he went in for his surgery there were people waiting to see him, and one of them literally got a knife out and just began stabbing him,” Mr Lamb said.
Police arrived at the scene in Eastwood Road North within minutes where they found the MP with multiple injuries and arrested a man.
“We knew it must be very serious because the paramedics had been working on Sir David for over two and a half hours and they hadn’t got him on the way to hospital,” Mr Lamb told the PA news agency.
At 14:13 an air ambulance arrived at a nearby sports ground to move him to hospital. However, members of his team began to fear the worst as paramedics remained at the scene.
Shortly before 15:00, Essex Police said Sir David had died.
At a press conference later Chief Constable BJ Harrington said officers and paramedics had worked extremely hard to save the MP.
Who is the suspect?
At 13:50 on Friday, Essex Police confirmed a 25-year-old man had been arrested immediately at the scene on suspicion of murder, and that a knife had been recovered.
Government sources have told the BBC he is a UK national who, from initial inquiries, appears to be of Somali heritage.
Whitehall officials say the suspect was not on their database of “subjects of interest”, according to BBC security correspondent Frank Gardner.
The suspect is in custody at an Essex police station and officers have said they are not looking for anyone else.
What was the motive?
The attack has been declared a terrorist incident by police.
The early investigation has revealed “a potential motivation linked to Islamist extremism”, according to Metropolitan Police’s Counter Terrorism Command.
The force says it is believed that the man acted alone but enquiries are continuing.
Speaking during a visit to the scene on Saturday, Home Secretary Priti Patel said the killing was “absolutely wrong and we cannot let that get in the way of our functioning democracy”.
What kind of enquiries will be under way?
Detectives and the security service MI5 will be delving deeply into the life of the suspect to understand how he reached his mindset, BBC home and legal correspondent Dominic Casciani says.
They will be looking at whether this was an attack by a “lone actor” or someone who is part of a network, he says.
If officers have recovered the suspect’s mobile phone, they will now be forensically examining its contents to uncover potential evidence of mindset and planning.
A phone – and any bank cards – will also help detectives track the suspect’s movements in the days and weeks before the incident. That in turn can lead them to CCTV so they can build a three-dimensional view of the suspect’s life.
The Met Police say officers are carrying out searches at two undisclosed addresses in London.
They have also appealed for any witnesses or anyone with CCTV, dashcam or doorbell footage to come forward.
What did witnesses see?
Anthony Finch, who was working nearby, told Sky News: “We arrived to do some work on the adjacent building… and at the point when I was crossing the road I saw an upset lady on the phone saying ‘you need to arrive quickly, he’s still in the building.'”
He said he had seen armed police, as well as an air ambulance and police helicopter. He told LBC: “It’s very odd and it’s very distressing, that’s for sure.”
Lee Jordison, who works for a local butchers and was on the scene shortly after the stabbing, told the BBC everyone in the area was in a state of shock.
“Something like this doesn’t happen – not in all the years I’ve been round this way.”
Who was Sir David Amess?
Sir David, who was married with five children, served as an MP for 38 years, initially in Basildon from 1983, before representing Southend West from 1997.
Raised as a Roman Catholic, he was known politically as a social conservative and a prominent campaigner against abortion. He was also a committed campaigner on animal welfare issues, and supported a ban on fox hunting.
The 69-year-old was a Brexit supporter and vocal champion for the town he represented, particularly in his long-running campaign to make Southend a city. He launched a new bid last month, after a city status competition was announced to mark the Queen’s platinum jubilee next year.
While he was never a minister, he was a member of numerous Commons committees, including the Health and Social Care and Backbench Business Committee.
Born in Plaistow, east London, in 1952, he went to school in the capital and taught at a school in the city. He was a recruitment consultant before becoming an MP.
He was knighted in the 2015 New Year’s Honours List for political and public service.