Yeah, really absence of evidence is evidence (though not proof) of absence, unless the absence of evidence can be explained as "well we haven't bothered trying

Yeah, really absence of evidence is evidence (though not proof) of absence, unless the absence of evidence can be explained as "well we haven't bothered trying to find evidence." (In other words, if I don't look in a box, then I don't have evidence that anything is in the box, but that's not evidence that the box is empty. If however I do look in the box and fail to find evidence of anything in it, that is evidence that the box is in fact empty.) They have presumably been looking for terrorists rather intensely.