Let's think about this logically shall we?
If the bombs are real, there is no reason why the FBI would not tell us that they are real.
If the bombs are not real, the FBI doesn't want to say so because they don't want us to let our guards down in case there is a real bomb still out there.
Therefore, by refusing to confirm or deny the if the bombs recovered so far are not real or not, this is the same as confirming the bombs are indeed not real.
If the bombs are real, there is no reason why the FBI would not tell us that they are real.
If the bombs are not real, the FBI doesn't want to say so because they don't want us to let our guards down in case there is a real bomb still out there.
Therefore, by refusing to confirm or deny the if the bombs recovered so far are not real or not, this is the same as confirming the bombs are indeed not real.