Pettygrudger is correct. This not claiming responsibility is Bin Laden’s SOP.
I think one of the things he may have been looking for in this case was his desire to play the innocent. I believe he wanted the PR event of having America attack him and being able to claim innocence. Actually a pretty effective strategy look at how many people were complaining about the ‘lack of evidence’ both in the west and especially in the Muslim world. Basically it was just a ploy to attempt to weaken the American resolve and international coalition. Bin Laden is no idiot.
Jelly