- Of the three main players, Litvinenko was the only one to ingest Polonium. Lugovoy and Kovtun actually left a more significant trail of Polonium around London, which - along with the fact that neither of them died - indicates they handled the Polonium but did not ingest it.
- If Litvinenko ingested Polonium, then it was murder. Not an accident caused during the smuggling of radioactive material. Unless you are seriously suggesting he swallowed radioactive material to get it through customs
- Detectives investigating the assassination eventually found three distinct radioactive trails. The first two were left by Lugovoy and Kovtun, during unsuccessful attempts to poison Litvinenko, who did not leave any trail on these two occasions. This means that Litvinenko only came into contact with Polonium on the third, successful, attempt to poison him with it.
This was a political assassination, planned and carried out by the FSB. Which by definition means that Putin was not only aware of it but approved. The FSB would not dare carry out such a potentially risky operation without Putin's blessing.
You cannot accuse me of being a shill, because I am simply stating what has been entered into legal record. The UK Government has stated they have evidence that Litvinenko was murdered by Lugovoy and Kovtun. Evidence strong enough for the British Government to start extradition proceedings, although this was of course denied by the Russian government.