Russians gather to commemorate the murder of investigative journalist Anna Politkovskaya 15 years ago on President Vladimir Putin's birthday, with her son saying that he still doesn't have a 'final understanding' of who ordered her killing. Politkovskaya, a fierce critic of Putin and the Kremlin's wars in Chechnya, was shot dead on October 7, 2006, in the entrance hall of her apartment block in central Moscow. IMAGES AND SOUNDBITES