Russia 'learned from its mistakes' as police still puzzled by spy poisoning
Russian intelligence learned from the Alexander Litvinenko murder to devise a near-perfect assassination method that has left British police still puzzled over how Sergei and Yulia Skripal were poisoned.
British authorities are increasingly convinced that Mr Skripal was exposed to a nerve agent planted in the luggage of his daughter Yulia, who was visiting from Moscow.
But they remain unclear of the precise method of delivery and when in Salisbury they were poisoned - known as the "ground zero" for the attack.
One well-placed source said: "We don't know where 'ground zero' is. We are just guessing at the moment."
A second source said the Novichok nerve agent was delivered in the form of a gel - rather than powder or gas - that transferred to the skin of the Skripals, delaying the effects of the poisoning for several hours.
They have discounted the theory that the nerve agent was somehow released into the air vents of Mr Skripal's car because of the likelihood the person involved would also have been exposed.
One source said the Russian FSB appeared to have learned from the mistakes made in the murder of Litvinenko in 2006 and how to cover its tracks without the need for an assassination squad to be deployed in the UK.
In the murder of Litvinenko, a dissident Russian spy, his assassins left a trail of radioactive Polonium 210 across London including in their hotel rooms, a hotel bar where he was poisoned, in restaurants, a lap-dancing club and on two aircraft.
The source said: "The luggage is looking increasingly likely. This all happened in less than 24 hours after Yulia arrived in the UK. Sergei wasn't in hiding so they didn't need to wait for Yulia to arrive. She unwittingly brought it with her, planted in the suitcase.
"There wasn't a hit squad on the ground. I really think they have learned from Litvinenko. His killers took a British Airways flight.
"They were leaving traces everywhere. With the attempted murder of Skripal, everything has been done back in Russia where they have complete control."
Security experts believe only a minuscule amount of nerve agent was required and that the Skripals were not even aware they had touched it in gel form.
The theory is it could have been left in a small pot in her luggage and later opened, or smeared on an item inside the bag, making it harder for experts to track the source definitively.
Meanwhile, 23 expelled Russian diplomats and their families flew out of London yesterday.
© Daily Telegraph, London