I think the “Chechens weren’t behind the bombings” hypothesis stims mainly from the fact that Russian authorities were doing “bomb defusion practice” at the apartments in question shortly before the explosion. They were never concrete on what they were doing, and it was rather mysterious.
How about one of the several hundred thousand Chechens who is not a terrorist? They were there before, and they’re there now. I bet we could even find some with government/administrative experience.
From memory and recent TV news reports. Around the time od the apartment bombings a small group of people, members of the Russian secret service were apprehended planting a bomb in an apartment building. Initial reports said the bomb was made of hexagen (?), supposedly a powerful explosive but the official explanation that emerged later was that it was just sugar and the spies (no one contests they were this AFAIK) were “testing” security.
Feel free to join in my cynical chorus of “Yea, right.” at this point.