Right. Just like they called to claim responsibility immediately after the attacks of 9/11/01 (which we were assured was pilot-error even though they'd been tracking the planes on radar -- until the second plane hit, at which point even off-the-charts morons wouldn't buy that story).
Homeland Security expects a terrorist group to call them immediately after the attack, to claim responsibility and then to actually prove that responsibility beyond a reasonable doubt.
Oh, wait... They didn't call, did they.
So, I guess the actual rule is that they will always call to claim responsibility for their attacks, except in those cases in which they don't call, but the main thing is that we don't worry, keep on shopping, and watch the fantastic entertainment provided by the television industry.
Strangely enough that pretty much IS the best thing we can do (keep the country running).
On the other hand I would like to think that I am smart enough to pull that off even if I was told the truth. So I do understand and agree with your fustration.
We did not have Homeland Security on 9/11.