What is known, and not known, about poisoning of ex-spy in Britain

LONDON (Reuters) - Former Russian double agent Sergei Skripal remains critically ill in hospital more than a month after he was poisoned with a nerve agent in the southern English city of Salisbury.

from Reuters: Top News http://uk.reuters.com/article/uk-britain-russia-explainer/what-is-known-and-not-known-about-poisoning-of-ex-spy-in-britain-idUKKCN1HC13O?feedType=RSS&feedName=topNews