London (CNN)Questions are swirling over how a Russian official turned British spy and his daughter ended up slumped over a shopping center bench in southern England on Sunday.
Sergei Skripal, 66, and his daughter, Yulia Skripal, 33, are in critical condition after being poisoned by a nerve agent in what UK police described Wednesday as a "major incident involving attempted murder."
While authorities have not yet named suspects or a motive for the attack, the case is a chilling reminder of a slew of mysterious Russia-linked deaths on British soil over the last decade.
A British inquiry found that two Russian agents poisoned Alexander Litvinenko at a London hotel bar in 2006 by spiking his green tea with the highly radioactive polonium-210.
Litvinenko died a slow and painful death over weeks after the poisoning and always insisted that Russian President Vladimir Putin and the Kremlin were responsible for what happened to him.
In a statement from his deathbed, he said: "You may succeed in silencing one man, but the howl of protest from around the world will reverberate, Mr. Putin, in your ears for the rest of your life."