States are increasingly using assassination to guard against the twin threats of terrorism and weapons of mass destruction.
The Skripal case shows how Russian intelligence services have the confidence to carry out shoddy operations, seemingly unconcerned about whether or not they will be discovered.
Donald Trump admires Russian President Vladimir Putin. But Putin's track record over his career reveals a serial liar, and presents damning evidence of complicity in multiple critics' violent deaths.
Putin's personal involvement is speculative, but report findings will cast a long shadow over Anglo-Russian relations.
A public inquiry says the murder of the former Russian spy was probably approved by Vladimir Putin. So how will the UK react?
Polonium's chemical properties made it the ideal secret weapon for the assassins of Alexander Litvinenko.