I’m sympathetic to the sentiment that making peace with Arabs is impossible (at least for the foreseeable future). I just wanted to point out that Chechens, while Muslims, are not Arab. Of course, similar ideologies are spread through the Muslim world. But we shouldn’t necessarily assume all Muslim ethnic groups are representative of Arabs.
The bombers’ mother lived through Soviet times, when the government was not to be trusted and the justice system was a farce, and Russia is not much better now. Add to that the paranoid thinking associated with radical Muslims, and it’s not hard to understand why she may be spouting these conspiracy theories.
More broadly, conspiracy thinking may be quite common in the region. After “Borat” made fun of Kazakhstan, the president of that country claimed it was some plot from Western governments to harm his country. Right after the older Boston bomber died, the president of Chechnya (republics in the Russian federation have presidents) suggested that the government killed him on purpose in order to calm society “at any cost.” He may not have read the news very closely, because it’s hard to survive when you’re shooting at police, lobbing explosives at them, and getting run over by your brother!
To answer the original question, it’s possible this will help some people see how absurd Holocaust denial is — hopefully that will happen. But the people who deny the Shoah are also the same kind of people who may believe that the bombers really were set up, and that there was some kind of government conspiracy. There is apparently a very serious Facebook page with 1000 or more members claiming that at least the younger brother is innocent.