A year ago on Friday, the Russian dissident and writer Alexander Litvinenko died in London of radiation poisoning.
Alexander Litvinenko was poisoned with polonium-210
It subsequently emerged that he had been given a massive dose of polonium-210. British police tried, unsuccessfully, to extradite the chief suspect, the former KGB operative Andrei Lugovoi.
Here, various people who were caught up in the story at the time describe how they got involved, and what they have learned since.
This is one year of my life without Sasha and it's still not easy to understand that he's not here.
Marina Litvinenko says every day her husband was ill was a "torture"
This last month, November, has been the hardest time for me. It is like everything that happened is happening again - it is so fresh. After he died, it was like each day I had fight to be alive. Each day was like torture. It was horrible.
After my husband died it became necessary for people to know that somebody can use this polonium as a weapon against humanity. We have to know about this material so that people will not use it again.
What is important now is the investigation into his death. I am absolutely sure that Lugovoi is not the only person. He had nothing against Sasha... but who was behind him? Because Russia refused to extradite him I feel there are strong powers behind Lugovoi.
My message to Lugovoi is: Come to London and defend yourself in a British court.
DEREK CONLON, PIANIST, MILLENNIUM HOTEL BAR
I was the pianist in the Pine Bar at the Millennium hotel. That was where Alexander Litvinenko was poisoned. He was given the polonium in a cup of tea.
Derek Conlon suffered the 3rd highest level of contamination
About an hour after he left, I sat at the same table, and drank coffee out of the same cup. They later found that although the cup had been through the dishwasher, it hadn't been cleaned properly.
A couple of days later they closed the bar - but no-one told me why.
It was only when I watched the news three weeks later that I learned about the poisoned Russian, and that I should contact the Health Protection Agency.
When I telephoned, I was told straight away to come into University College Hospital where doctors took samples of my urine and blood and sent them off for testing.
A week later I was called back to the hotel, and shown into a room where there were two doctors. The doctor said: "We have some bad news for you, the results are a little high."
I later learned that I had suffered the 3rd highest contamination of all the people affected.
I was really worried at first - I thought I might get cancer. But I've just had my last test and they have found that most of the stuff is out of my body.
As time has gone on I've decided that I will use the experience to make the most of my life.
I wrote a song - "A sad and lonely man" - based on my experience. It came second in the jazz and blues section of the UK Songwriting Contest.
PC ANDY WIGLEY, BARNET POLICE
One of my roles is to liaise with Barnet Hospital and when I got the call on my mobile saying a Russian spy had been poisoned, I thought my boss was joking.
PC Andy Wigley held Litvinenko's hand in hospital
I was taken up to the private ward and introduced to his wife. She told me the KGB was trying to kill him - they had been to the hospital a couple of times with what they originally thought was food poisoning. I then went through to the bedroom and there he was on the bed. He was yellow and had lost his hair.
I held his hand and chatted to him - he was sick about six times - once on my arm. He was genuinely terrified: once he heard a helicopter, and thought it was Russian special forces trying to kill him.
He appeared to know what was happening to him: he said he was a retired KGB spy himself and was convinced he had been poisoned with radioactive lithium. That's what the KGB used, he said.
Although I hadn't believed it at first about being a spy, Mr Litvinenko told me certain information when I was there. I can't repeat what he said, but it convinced me he was telling the truth.
I stayed with him until they moved him to UCHL hospital. Afterwards we helped secure the Litvinenko house while it was tested for radioactive contamination. I got a commendation last summer for the way I helped handle the situation.
Looking back on it now I can see he was terrified for good reason. Although as a police officer you have to distance yourself from some things, looking back on it I feel really sorry for the poor bloke. He must have been in awful pain.
NIGEL LIGHTFOOT, CHIEF ADVISER, HEALTH PROTECTION AGENCY
It was a huge job to trace the contamination and find out who had been affected. During the first two weeks I worked 18 hours a day, six days a week.
Professor Nigel Lightfoot conducted his investigation in the public gaze
Our teams eventually traced the contamination to around 40 separate premises. It was in hotels, a sushi bar, offices - basically everywhere the suspect had been.
It was like following a trail around London that got bigger all the time. Every time we identified a new site we had to seal it off, test for radiation and run a risk assessment.
In the end we calculated about 1,500 people might be at risk, of whom 17 were actually found to be contaminated with polonium, which puts them at a slightly higher risk.
It was all new territory for us: none of this incident had been rehearsed. But we learnt some valuable lessons. The first is that we were right to keep the public informed. It's important that people have the information that they need so that they can make their own risk assessment. That way you avoid panic.
And the other thing we learned was that you need a large team for this sort of incident - we had 400 people working at its peak - and they all need to work together.
ALEX GOLDFARB, LITVINENKO FRIEND AND CAMPAIGNER
On the first anniversary of Sasha's death on Friday, I will read out his last statement in front of the hospital where he died.
Alex Goldfarb is convinced that President Putin ordered the murder
It will be a rhetorical statement - when he died he did not know about polonium and the cover-up perpetuated by the Russian government and Mr Putin personally.
Putin was frustrated because he wasn't able to extradite Litvinenko to Russia, and he was mad at the British, so he decided to get him by other means.
When Sasha first got ill I discounted it because the doctors didn't think it was serious at first. I came to the hospital on the 14th day - the doctors still thought he had a stomach bug.
The day afterwards, it was official - as soon as it was clear it was polonium we knew he was doomed. He took one sip of the tea. But if he had taken two sips he would have died within the week.
I write in the book ("Death of a Dissident" by Alex Goldfarb and Marina Litvinenko) that our whole generation was turned into neurotic by fears of nuclear death by cold war, and now I saw it with my own eyes. It was our worst nightmare when he died.