Sergei Skripal was a Russian double agent who served in Russia's main military foreign-intelligence service, GRU (Glavnoye Razvedyvatel'noye Upravleniye). After his arrest and four years of prison for spying for Britain's espionage service, Skripal was included in a 2010 spy swap between the U.S. and Russia on an airport runway in Vienna. In turn, he was granted refuge in the UK.

In early March, Skripal's daughter, Yulia, was visiting from Russia.

On March 4, the pair were found unconscious on a bench outside a shopping center in the southern English city of Salisbury.

Sergei and Yulia Skripal, as well as one of the first police officers responding to the scene, all remain hospitalized in critical condition.

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Less than one hour ago, UK Prime Minister Theresa May addressed Parliament and disclosed a Novichok class of nerve agent was used in the attack.

The Novichok class of agents are reportedly developed by Russia in an attempt to circumvent the Chemical Weapons Treaty. The agents have reportedly been engineered to be undetectable by standard equipment and to defeat standard chemical protective gear. Like other nerve agents, the Novichok agents act by inhibiting the enzyme cholinesterase.

• Novichok agents may be dispersed as an ultra-fine powder as opposed to a gas or a vapour.
  
  
• Novichok agents may consist of two separate ‘non-toxic’ components that, when mixed, become the active nerve agent.
  
  
• The primary route of exposure is thought to be by inhalation.