The family of the policeman killed in the Westminster terror attack has thanked those who tried to save his life, and said they care that the officer is remembered for his "selfless bravery and loving nature".
Unarmed Pc Keith Palmer was stabbed by terrorist Khalid Masood in an 82 seconds-long rampage in London which killed three other people who had been on Westminster Bridge.
Masood drove his car along the bridge at speed, mowing down pedestrians, and was shot dead by police after he stormed the parliamentary estate armed with two knives on Wednesday afternoon.
Hero MP Tobias Ellwood was among those who tried to save Pc Palmer's life.
Addressing those who helped, the officer's family said: "There was nothing more you could have done."
In a statement released on Saturday night they said: "We have been overwhelmed by the love and support for our family, and most especially, the outpouring of love and respect for our Keith.
"We want to thank everyone who has reached out to us over the past few days for their kindness and generosity.
"The police have been a constant, unwavering support at this very difficult time. It has made us realise what a caring, strong and supportive family Keith was part of during his career with the police. We can't thank them enough.
"We would also like to express our gratitude to the people who were with Keith in his last moments and who were working that day. There was nothing more you could have done.
"You did your best and we are just grateful he was not alone. We care about him being remembered for his selfless bravery and loving nature. We miss him so much, but we are also incredibly proud of Keith."
Police have released specific timings of Masood's murderous spree, showing he took just 30 seconds from mounting the pavement on the bridge to crashing into the perimeter fence at Parliament.
Within less than a minute he made his way on to the parliamentary estate, attacked Pc Palmer, and was shot.
Police believe Masood acted alone on the day of the attack, and warned that while they continue to investigate why he committed the atrocity "that understanding may have died with him".
Deputy Assistant Commissioner Neil Basu, the senior national co-ordinator for UK counter terrorism policing, said: "We still believe that Masood acted alone on the day and there is no information or intelligence to suggest there are further attacks planned.
"Even if he acted alone in the preparation we need to establish with absolute clarity why he did these unspeakable acts to bring reassurance to Londoners, and to provide answers and closure for the families of those killed and the victims and survivors of this atrocity.
"We must all accept that there is a possibility we will never understand why he did this. That understanding may have died with him."
He said officers are working to establish whether Masood was "a lone actor inspired by terrorist propaganda or if others have encouraged, supported or directed him".
He added: "Whilst the attack lasted only 82 seconds it will remain in the memories of many forever."
Fears Masood was groomed for extremism in prison have heightened after it was claimed he turned to Islam behind bars.
Counter-terrorism officers have spent days piecing together what led the 52-year-old to shed his birth name and later unleash carnage on the capital.
Only one man, 58, arrested in Birmingham remains in police custody after a 27-year-old man was released with no further action on Saturday.
A total of 11 people were initially held after raids across the country.
The Saudi Arabian embassy in London said Masood worked in the country, home to some of the most virulent Islamic extremism, for several years, raising the possibility he was radicalised overseas.
A childhood friend of the man then known as Adrian Elms told The Sun newspaper he first emerged as a Muslim after serving a jail sentence.
His abrupt religious conversion will fuel concerns about the rising threat of criminals being brought under the influence of hardened jihadists while in prison.
Ministers have announced plans to create specialist units within jails to tackle what a government-ordered review last year concluded was a "growing problem".
His route to extremism could have also come from a stint living in the Middle East.
The Saudi embassy said Masood lived in the country between November 2005 and 2006 and April 2008 and April 2009, during which time he worked as an English teacher on a work visa, travelling to the country again for five days in March 2015.
It said in a statement: "During his time in Saudi Arabia, Khalid Masood did not appear on the security services' radar and does not have a criminal record in the Kingdom of Saudi Arabia."
Details of Masood's history of criminality have continued to come to light, suggesting a propensity for violence which laid the groundwork for his armed rampage.
The middle-aged Muslim convert was born in Kent, but moved around the country and used a variety of aliases including Adrian Russell Ajao.
Masood was known to police and MI5 but was a "peripheral figure" who was not implicated in any current probe.
He had convictions for assaults, including grievous bodily harm, possession of offensive weapons and public order offences.
Mr Ellwood and security minister Ben Wallace have been appointed to the Privy Council for their roles in responding to the atrocity.
Masood's victims on the bridge included US tourist Kurt Cochran and his wife Melissa, from Utah, who were on the last day of a trip celebrating their 25th wedding anniversary. Mr Cochran was killed and Mrs Cochran was badly injured.
Aysha Frade, who worked in administration at independent sixth-form school DLD College London, in Westminster, also died. She is believed to be a 43- year-old married mother of two.
Leslie Rhodes, a retired window cleaner from Clapham, south London, died from injuries sustained in the attack. He was described by neighbours as a "lovely man".
Two people remain in hospital in a critical condition, one with life-threatening injuries.
Pc Kristofer Aves and another police officer hurt in the attack are also in hospital with "significant injuries".
Police said armed patrols would take place around Wembley Stadium and extra officers would be at the ground when England played a World Cup qualifier against Lithuania on Sunday.
There will also be a minute's silence before the 5pm kick-off.