Putin's presidency thrives in times of international tensions. His single most important tool in the box is 'us vs them' narrative/victimhood (where is da proofs? we dindu nuffin). So he goes out, sets little geopolitical fires here and there, collecting harsh words and sanctions from the EU/UK/US, plugs them into his state controlled media, goebbels effect occurs, his approval ratings to through the roof. I am not even excluding the possiblity that the attack was timed for presidential elections cos no matter how many kids are left to burn alive in Kemerevo, russians always look up to the guy who stands up against western provocation and aggression