If it wasn't for that, then yes I'll have to say that the Chechens were behind the apartment bombings in Moscow.
But since he got poisoned, it's obvious that the FSB did it.
Putin is ruthless enough to do something like that as long as he thinks it benefits Russia in the long run.
The poisoning doesn’t tell us.
Russians like Putin are absolutely ruthless in getting revenge against “traitors”.
It would be treason to reveal that the FSB did the bombing. But someone like Putin would see it as an even greater treason to falsely claim the FSB did it.