Are you suggesting that if the FSB were responsible for some, or all, of the Moscow bombings, then that would be OK, since the peole they were smearing were already killers?
The big IF! One could apply the same insinuation to FBI about 9/11 or to Mossad about bombings in Israel or about you beating your wife. To insinuate is easy, cheap and it is hard for the accused to prove the negative.