Why was ex-spy Alexander Litvinenko a marked man?

“You may succeed in silencing me but that silence comes at a price,” Litvinenko said in the statement from his deathbed.

“You may succeed in silencing one man but the howl of protest from around the world will reverberate, Mr. Putin, in your ears for the rest of your life.”

READ MORE: Did Russia put polonium in spy’s tea?

It’s an allegation the Kremlin has never really managed to shake off.

Perhaps the killers hoped it would not have been detected by British investigators. Or perhaps they wanted to send a message, pointing the police towards an executioner they knew would never be held to account?

But the biggest question of all is whether the killing was ordered by the state, or was the work of rogue elements within it.

Perhaps only President Putin, himself a former KGB agent, has the answer to that.

CNN