Questions mount over Russian spy poisoning
The international community has rallied around Britain in recent days in pointing the finger at Russia for the poisoning of Sergei Skripal and his daughter Yulia.
But as the pressure grows, not everyone is convinced of President Putin's regime's guilt and questions are mounting about how the nerve agent was delivered and exactly who ordered the hit.
The Russian government: While it still emphatically denies any wrongdoing, intelligence bosses seem convinced that the Russian government could be the only source of the nerve agent Novichok.
Novichok, which means newcomer in Russian, was developed by the Soviet Union in the 1970s as a chemical weapon that would be more powerful, harder to detect and exempt from the Chemical Weapons Treaty.
Russia refused to respond to Theresa May's demands for it to explain why Novichok was used in the attack in Salisbury, or to explain how and when it may have lost control of its stocks of the nerve agent.
Vladimir Uiba, the head of the Federal Medical and Biological Agency, would not say if Russia inherited any amounts of Novichok from the Soviet Union and whether they were destroyed.
Foreign Secretary Boris Johnson, writing in the Washington Post, said: "There is a reason for choosing Novichok. In its blatant Russian-ness, the nerve agent sends a signal to all who may be thinking of dissent in the intensifying repression of Putin's Russia.
"The message is clear: We will find you, we will catch you, we will kill you - and though we will deny it with lip-curling scorn, the world will know beyond doubt that Russia did it."
The Russian mafia: Labour leader Jeremy Corbyn was among those voicing the possibility that rogue elements within the Russian state might be behind the assassination attempt, warning people not to become "overwhelmed by emotion and hasty judgement".
Writing in the Guardian, he condemned the "horrific" incident but insisted: "A connection to Russian mafia-like groups that have been allowed to gain a toehold in Britain cannot be excluded."
The British: Russian MP Vitaly Milonov, of the ruling United Russia Party, claimed the poisonings were orchestrated by the British Government to make its "anti-Russia" policy more palatable to the public and businesses.
He claimed Mr Skripal was "useless" to the Russian state and there was no value in poisoning him and likened it to a "British TV drama".
He told the BBC: "My personal point of view (is) that Theresa May and her colleagues they have created a fake story because they need an explanation to British people and British business why they are going to perform some anti-British steps in favour of United States policy against Russia.
"So, they had to make this fantasy. They had to kill, to try to kill, this poor pensioner, useless for us."
In the wake of the discovery of 66-year-old Mr Skripal and his 33-year-old daughter slumped on a bench in a shopping centre, health officials feared as many as 131 locals could have been exposed to the toxin.
Multiple theories have been put forward as to how the deadly nerve agent was administered.
In Yulia Skripal's suitcase: Ms Skripal returned from a visit to her native country the day before the attack, and intelligence chiefs believe an item of clothing, cosmetics or a gift may have been laced with the poison, the Telegraph reported.
She landed at Heathrow at 2.40pm on March 3, and she and her father were found collapsed at 4.15pm the following day.
Counter-terror police and M15 now allegedly believe it is more likely that the Novichok was planted on Ms Skripal before she returned than an assassin being deployed to the UK.
The car door: Forensic scientists in hazmat suits have been observed combing Mr Skripal's BMW for traces of the nerve agent, and one theory is that the substance was smeared on the door handle in powder form.
The grave: A forensic tent was erected over the grave of the spy's late wife Liudmila who died in 2012 and is buried in a cemetery in Salisbury - the ashes of the couple's son Alexander who died last year.
The bodies have not been exhumed although objects have been removed from the site.
The pub and the restaurant: Mr Skripal and his daughter went for drinks at the Mill pub before dining at the Zizi restaurant before they were found collapsed.
Traces of the nerve agent were found at both sites and guests at the two venues were advised to thoroughly wash their clothes and wipe any of their personal effects such as mobile phones, bags and jewellery with baby wipes over fears they may have been exposed.
The mystery couple: The police have issued an appeal to the public over any information of anyone acting suspiciously on the night of the alleged attack.
So far, CCTV from a nearby Snap Fitness 24/7 gym has yielded images of a man and a woman walking away from the area a 3.47pm - just moments later the Skripals were first reported "acting strangely" by a member of the public.
Police have said they are keen to speak to the man and woman in the footage.