Conservative MP Sir David Amess died after being stabbed at his constituency surgery in Essex on Friday afternoon.
The attack, which happened just after midday on October 15, shocked the nation while MPs have united to express their sadness and affection for a colleague and a friend.
Here's how the attack unfolded and what we know so far.
Read more:Live updates as Boris Johnson pays tribute to 'kind and gentle' man
Sir David, the MP for Southend West, was meeting constituents at a regular surgery at Belfairs Methodist Church in Leigh-on-Sea when the stabbing occurred.
Police were called to the scene in Eastwood Road North shortly after 12.05pm on Friday, where they found the 69-year-old injured.
He was treated by paramedics but died at the scene.
Aerial footage showed multiple police officers outside the church and an air ambulance was also seen.
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Who did police arrest?
A 25-year-old man was arrested on suspicion of murder after officers arrived at the scene and a knife was recovered, Essex Police said.
The Telegraph has reported that the suspect is of Somalian heritage and he was seen by a witness being taken away by police in a calm and compliant manner. The Telegraph said security sources had confirmed that the suspect was believed to be of Somalian heritage, but police were still seeking to establish a motive for the attack.
The BBC said official sources confirmed that detectives have established the individual is a UK national, seemingly of Somali heritage.
He is in custody and police said they were not looking for anyone else. The Essex force has appealed for any witnesses or anyone with CCTV, dashcam or doorbell footage to come forward.
How is the investigation being progressed?
Ben-Julian Harrington, chief constable of Essex Police, said the investigation was in its "very early stages" and was being led by officers from the specialist Counter Terrorism Command. It will be for investigators to determine whether it was a terrorist incident and police will "keep an open mind", said Mr Harrington.
The emergency services arrived on the scene within minutes of being alerted and found Sir David had suffered multiple injuries.
The full statement said: "At just after midday today, Essex Police were called to reports of a stabbing in Eastwood Road North, Leigh-on-Sea. The response of the emergency services to this incident was immediate and our officers arrived on scene within minutes.
"When they arrived they found Sir David Amess MP, who had suffered multiple injuries. This was a difficult incident, but our officers and paramedics from the East of England Ambulance Service worked extremely hard to save Sir David. Tragically, he died at the scene. A 25-year-old man was arrested immediately at the scene on suspicion of murder. He remains in custody.
"A knife was also recovered at the scene. The investigation is in its very early stages and is being led by officers from the specialist counter-terrorism command."
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Were there any witnesses?
A local man described the horrific scenes at the church, saying he heard a woman at the scene desperately telling police, "get here as soon as you can, he's still in the building".
Local electrician Anthony Gavin Fitch, 38, told The Mirror: "I heard it was a stabbing from a lady who was inside the church at the time. She was upset and said David Amess had been stabbed three times. She said there was an altercation and then the suspect stabbed him."
Mr Fitch first realised something was wrong when he parked outside Belfairs Methodist Church and heard a woman on the phone to the police.
He said: "I was exiting my vehicle to look at a job after parking up outside the church. As I was walking across the road I saw a few people sitting on the wall outside the church and one was on the phone to the police. She was saying 'get here as soon as you can, he's still in the building'. She was wearing a badge with the Tory logo on it.
"Armed police, ambulances and an air ambulance turned up. I saw police taking the suspect out and putting him in the back of a police van. He was taken away by two officers with armed police behind him. He didn't make any noise."
Mr Fitch said the stabbing was even more shocking because it took place in what was seen as a safe neighbourhood.
Lee Jordison, 40, who witnessed the aftermath of the attack on Sir David, was told that a woman came out of the church screaming "he's not breathing".
He told The Mirror: "I was working in our shop about 100 metres away when I was alerted to ambulances and police cars going past. I took a walk down the road and saw police setting up a cordon. I spoke to someone walking up the road and they said there was a stabbing in the church.
"There were lots of ambulances and police with machine guns. I heard from a couple of people that a lady came out screaming phoning the police saying 'please get here quickly he's not breathing'.
"One person said David Amess was there and then I heard from someone else that the person who was stabbed was the MP. We were like, 'oh my God'."
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.
The 69-year-old animal lover was known politically as a social conservative having campaigned against abortion, supporting the ban on fox hunting and supporting Brexit. He'd led a long-running campaign to make Southend a city which received a new boost after a city status competition was announced to mark the Queen's platinum jubilee next year.
He was never given a ministerial position but was a member of numerous Commons committees, including the Health and Social Care and Backbench Business Committee.
He was knighted in the 2015 New Year's Honours List for political and public service.
What does it mean for MP security?
House of Commons Speaker Sir Lindsay Hoyle paid tribute to David Amess, calling him "a lovely man, devoted to his family, to Parliament and his Southend West constituency".
Sir Lindsay added that, over the coming days, "we will need to discuss and examine MPs’ security and any measures to be taken".
He later spoke to Radio 4 and said: "I am doing my surgery tonight. I recognise some MPs are not doing theirs. What we can't do is give in to these people, people who don't believe in our values, don't believe in what we do.
"I believe the electorate needs to be able to communicate with the people who have been elected. It is part of our democratic process, that relationship.
"We don't knee-jerk reaction. What we want to do is make sure MPs can carry out their duties. We have got to make sure MPs are safe."
MPs' security has long been a serious issue but ramped up after the killing of Labour's Jo Cox in 2016. Following that attack, all MPs were offered panic buttons, extra lighting, additional locks and emergency fobs at their homes and constituency offices. Official data shows the amount spent on such measures rose from £171,000 in 2015/16 to £4.2m in 2017/18.
Home Secretary Priti Patel also paid tribute to Sir David before adding that she would provide an update "in due course" on questions around the safety of MPs. She said on Twitter: "Questions are rightly being asked about the safety of our country's elected representatives and I will provide updates in due course. My heartfelt thoughts and prayers are with David's family and friends.
"I am devastated we have lost Sir David Amess. David was not only a fellow Essex MP, but a kind and loyal friend. David served the people of Southend with endless passion, energy and integrity. That he was killed while going about his constituency duties is heartbreaking beyond words. It represents a senseless attack on democracy itself."
A spokesman for the Home Secretary later added: "This afternoon, the Home Secretary chaired a meeting of the Police, Security and Intelligence Agencies to discuss the tragic incident in Southend and the ongoing response. She also spoke to the Speaker of the House of Commons."
"The Home Secretary has asked all police forces to review security arrangements for MPs with immediate effect and will provide updates in due course."
The Senedd issued its own statement about security arrangements for Welsh MSs, saying there would be a meeting next week for staff and members to look at future security arrangements. A spokesman said: "We are deeply shocked and saddened by the death of Sir David Amess. We take the safety of everyone involved with the Senedd extremely seriously. Members have been informed of a hybrid drop-in session with security staff early next week to discuss and advise on any concerns."
Where was Boris Johnson and what did he have to say?
Prime Minister Boris Johnson, who'd been holding a cabinet meeting in Bristol when news of the stabbing broke, arrived back at No. 10 late afternoon. The flags were flying at half mast over Downing Street as he arrived home.
The PM paid tribute to "one of the kindest, nicest, most gentle people in politics". Mr Johnson said: "David was a man who believed passionately in this country and in its future. And we've lost today a fine public servant and a much-loved friend and colleague, and our thoughts are very much today with his wife, his children, and his family."
Dan Norris, Bristol’s metro mayor, was with Boris Johnson when the news broke and said this afternoon's events would have to change the way British politicians work in the future in order to protect their own safety.
He was in a meeting with the PM at the Rolls-Royce factory in Bristol on Friday afternoon and said: "I was with the Prime Minister today when he found out and he mentioned something significant had happened with a colleague and that he needed to leave. I found out later on like everyone else what had befallen David."
Has this happened before?
Sir David is the first serving MP to be killed since Labour's Jo Cox was murdered in West Yorkshire in 2016. They are two of six British MPs to be killed in office since the Second World War.
Ian Gow, a Conservative MP, was killed by an IRA car bomb outside his home in East Sussex in July, 1990.
Sir Anthony Berry was killed in the IRA bombing of the Grand Hotel at the Conservative party conference in Brighton in October, 1984.
Robert Bradford, an Ulster Unionist and a Methodist minister, was assassinated by IRA gunmen in November, 1981, at the age of 40.
Airey Neave, the Conservative shadow Northern Ireland secretary, was blown up one afternoon in March, 1979, after his booby-trapped car exploded in the Palace of Westminster.
How have people reacted?
Flags are flying at half mast at Downing Street and at the Senedd in Cardiff while tributes are coming in from across the political spectrum.
Labour leader Sir Keir Starmer said: "Today is a dark and a shocking day - the more so because heartbreakingly, we've been here before."
Mark Drakeford, Wales' First Minister, said: "Deeply saddened to hear about the death of Sir David Amess. A truly despicable and horrifying act. My thoughts are with his friends, family, and constituency staff during this distressing time."
While the Secretary of State for Wales, Simon Hart, said: "The news that my colleague David Amess has been stabbed and killed whilst serving his constituents is a desperate tragedy for his family, friends & community. It’ll raise many questions but for now I know we’ll all be thinking of his family and remembering his kindness and dedication."
Brendan Cox, Jo Cox's husband, has been a prolific campaigner since her death, working to help families and survivors of terrorism get the rights they deserve. He tweeted this afternoon: "My thoughts and love are with David’s family. They are all that matter now. This brings everything back. The pain, the loss, but also how much love the public gave us following the loss of Jo. I hope we can do the same for David now."
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