Was the release of an Osama bin Laden audiotape last week a signal to Yemeni terrorists to initiate the cargo-plane bomb plot? Authorities are investigating the possibility, as they suspect that bin Laden and other al Qaeda leaders in Pakistan are guiding the Yemen-based al Qaeda in the Arabian Peninsula. This increased collaboration between the groups has officials particularly worried about bomb plots in Europe which they first detected months ago; the U.S. government’s travel advisory to Americans in Europe remains in place. Of bin Laden’s role, one senior U.S. intelligence official says, "Everyone is playing in concert with his larger guidance. This is part of their long-term strategy."