This is believed to be the last picture (l) of PC Keith Palmer before he was fatally stabbed
The picture was taken by American tourist Staci Martin who posed with the officer 45 minutes before he was fatally attacked on Wednesday by Khalid Masood, whose birth name was Adrian Russell Ajao, in the yard outside the Palace of Westminster.
Ms Martin, who was visiting from her home in Florida, told how the policeman was “really nice” when she approached him to ask for a photo together in front of the UK’s heart of democracy.
She told ABC News: “It's my first time in London and I see his hat and I'm like I have to take a picture of him with his hat.
"I walked up to him and said 'do you mind if I take a picture?' He said 'no problem', he was really nice."
Less than an hour later, Ms Martin was travelling in a taxi when she heard there had been a shooting and saw emergency vehicles and a helicopter overhead.
When PC Palmer’s photo was released by police after confirming he had died at the scene, she immediately recognised him from her photo.
MP Tobias Ellwood rushed to give CPR to PC Keith Palmer
She believes the picture is one of the last photos taken of him before he died.
The American woman said she feels “obligated” to get the photo to his family.
She added: “I just want to make sure they have that of him.”
Seconds after Masood stabbed PC Palmer with two knives he was shot by Defence Secretary Michael Fallon’s security detail and despite paramedics trying to save the attacker, he also died at the scene in New Palace Yard.
Get Quotes on Home Insurance
Tory MP Tobias Ellwood, a former Army captain, rushed to help PC Palmer, defying orders to go back inside to carry out CPR on the policeman before paramedics arrived.
Moments before Masood, previously known as Adrian Elms, drove his hired Hyundai 4×4 along the pavement on the west side of Westminster Bridge, knocking down pedestrians.
London terror attack victims Fri, March 24, 2017
ISIS have claimed responsibility for the London attack that killed four people
1 of 10
Three of those pedestrians have now died, including British woman, Aysha Frade, a 43-year-old Spanish teacher who was picking up her two daughters from school when she was hit and killed.
American tourist Kurt Cochrane, a 54-year-old musician from Utah who was on the last day of a dream European trip, was also killed as he was thrown onto some concrete steps below the bridge.
A 75-year-old man, named this morning as former window cleaner Leslie Rhodes from Streatham, south London, died in hospital yesterday after having his life support pulled.
Tributes to PC Palmer and the other victims were laid down by the public outside Parliament
A vigil was held in Trafalgar Square on Thursday night
On Thursday, terror group Islamic State (ISIS) claimed Masood had carried out the attack on behalf of him.
Police have made 10 arrests so far, with eight made overnight after Wednesday’s attack and two “significant” arrests made on Thursday night.
All but one woman, who was released on bail, remain in custody.
Police are now turning their investigation on to how Masood was radicalised after being born in Dartford, Kent, and growing up in the picturesque coastal town of Rye in East Sussex.
He had been living in Birmingham where he set up his own business but had lived in Saudi Arabia for four years where he converted to Islam.
When he moved back to the UK he lived in Luton in Bedfordshire and had previously been in a British jail for four years, which police believe could be where he was radicalised, or it may have been in the Middle East.