Was the attack the work of rogue Russia security agents or a chilling message from Putin?
For a man who lived in a modest semi-detached house in a cul-de-sac in the genteel cathedral city of Salisbury, Sergei Skripal had a very immodest past. Some reports suggest that the former officer with Russias military intelligence service, the GRU, shared with MI6 the identities of as many as 300 Russian agents during his time as a double agent.
At his trial, the Federal Security Service (FSB, the successor to the KGB) compared Skripal to Oleg Penkovsky, who was executed in 1963, and who history records as one of western intelligences most valuable assets.
After his release in 2010, in the largest spy swap since the end of the cold war, Skripal would have been all too aware of how his colleagues viewed him. Many in the FSB are fond of quoting the motto of Smersh, Stalins counter-intelligence unit: Death to spies. That he came from the GRU only made things worse.
The Russian state is a strange construction, said Sir Andrew Wood, a former British ambassador to Russia, now an associate fellow at Chatham House. The FSB is not a monolithic organisation. There are elements within it like the GRU, which is a sort of rival to the FSB.
Many within the FSB are ultranationalists. The assassination of a traitor shortly before this weeks presidential election would have made a nice gift for one of their most famous alumni, President Vladimir Putin, who is seeking to win 70% of the vote.
But while Wood has little doubt that the brazen attempted murder of Skripal, 66, and his daughter, Yulia, 33, an operation using a rare form of nerve agent available to only a few foreign states, can be laid at Russias door, he questions whether Putin would have sanctioned it directly.
I dont doubt it had general approval from senior heads thats the system hes created. Since 2012 Russia has been going backwards, rejecting economic reform and better courts in favour of renewed state control and repression, a fear of anything that is other. Its the revival of Stalinism and the idea that Russia has the right to dominate its neighbours.
In this climate, former FSB officers now working in the murky world inhabited by ex-spies feel they can act with impunity.
Whether Skripal had an inkling his life was in danger is unclear. There has been speculation in police circles that he received an Osman notice before he was attacked. These are warnings handed by the security services to people they fear may be targeted. But Skripal seems not to have made any changes to his lifestyle: hardly the action of someone in fear for their life.
The are also claims that considerable amounts of money were found in his bank account and that mobile phone records connect him to the former MI6 agent who recruited him. Again, none of this can be confirmed.
But quite a lot is known about the agent in question. At the time of Skripals arrest in 2004, the Itar-Tass news agency reported that the MI6 officer was working in the British embassy in Tallinn and had been responsible for recruiting scores of Russian intelligence assets. According to the FSB, these included a Russian security service officer, Vyacheslav Zharko.
Its at this point that the past and the present collide. The attempted murder of the Skripals has drawn comparisons with the fatal poisoning of the spy Aleksandr Litvinenko, who was on the payroll of the exiled oligarch and Putin critic, Boris Berezovsky.