Zawahiri has not been seen or heard since December 2009, “the longest gap he has had in nearly six years,” according to Ben Venzke of the IntelCenter, which monitors al Qaeda messages for governments, businesses and the media.

A US official said there is “no reason” to believe that Zawahiri has been killed or injured in recent months but that “it is possible” he and other al Qaeda leaders “have new concerns about their security.”…

Some intelligence analysts believe such absences precede major terror attacks by al Qaeda.

“I don’t like it, it’s too quiet,” said another person who monitors websites for al Qaeda and terror-related messages.