Osama bin Laden hasn't made a single peep publicly in over a year - his longest absence since 9/11. The ghoul's eerie silence is both disturbing - and odd - for the leader of a global terrorist organization hellbent on changing world order.

So what is Public Enemy No. 1 up to? Osama's glaring absence from the world stage means one of three things: a) We've been closing in on him and he's gone deeper underground; b) He's lulling us into complacency while planning another big terrorist strike, or c) He's dead.

It's hard to believe the world hasn't heard a word from Osama since Dec. 27, 2004, the day of the release of his audiotape anointing Abu Musab al Zarqawi as al Qaeda's head honcho in Iraq. (Since it took time arriving from Osama's hideout, the tape probably was made even earlier in the fall).

Earlier that December, Osama released a video calling for al Qaeda to strike Persian Gulf oil supplies and warning the apostate House of Saud that they risked a popular uprising.

Since these two cameos, not a single evil "Osama-gram" of any kind . . .

Not that al Qaeda has been completely mum on the propaganda front since late 2004. Stepping into the media limelight as recently as last Friday has been Osama's deputy and the "brains" of al Qaeda, the bespectacled Egyptian physician Ayman al Zawahiri.

Most notably, Zawahiri insisted in a videotape last September that Osama was, in fact, alive and well, saying: "Al Qaeda for holy war is still, thanks to God, a base for jihad. Its prince Osama bin Laden, may God protect him, still leads the jihad."

You have to wonder why al Qaeda's mythical leader couldn't find his way to the camera himself to tell us all of this instead of relying on Zawahiri? Hmmm . . . makes you wonder.

Of course, without irrefutable evidence, no political leader has been willing to declare Osama dead. Pakistani President Pervez Musharraf said he didn't know whether Osama was dead or alive, adding that he didn't want to speculate over the killer's fate.

In Afghanistan, the U.S. commander, Gen. Karl Eikenberry, insists that Osama is still considered alive - and the hunt continues. His boss, Defense Secretary Don Rumsfeld, recently said that he doubts Osama is still capable of running al Qaeda's global terror operations.

Even Islamists, in some of their numerous Web sites, have begun to speculate on Osama's demise.

Of course, until we have proof positive of a demise, we have to assume Osama is "at large and in charge." Any assumption short of that would be foolhardy - and potentially deadly.

It's very possible that Osama, a fugitive on the run and under continuing pressure by U.S. forces, has gone incommunicado along the rugged Afghan-Pakistan border. He may have also fled into safe haven in neighboring Iran - or even left the region completely.

By lowering his profile, Osama may also be trying to lull us into complacency four-plus years after 9/11, while he plans the next big attack. "Out of sight, out of mind" could lead to America dropping its guard; complacency is as big a threat to our security as Osama and al Qaeda.

It's also possible that Osama has gone "belly up." Although there is disagreement about whether Osama has kidney problems, few consider him a picture of health. Hanging out in caves for four years probably hasn't improved his condition -physical or mental.

All that said, the fact remains that Osama is al Qaeda's trademark and the source of inspiration to the Islamic terrorist movement. It makes no sense for him to disappear from view for over a year while his phalanxes are waging a bloody jihad from the London's subways to Baghdad's streets to Bali's tropical isle.

Osama's prolonged absence - and the increasing prominence of his evil twin, Zawahiri, can only reasonably mean one thing: Osama is either dead, sick or incapacitated - all unsuitable states for propaganda productions.

Osama's ultimate demise would certainly be great news for this country - and the world. In fact, although no guarantee, proof of Osama's death just might be the beginning of the end of al Qaeda.

Which, of course, gives al Qaeda good reason to never admit it.

Unfortunately, al Qaeda isn't just Osama bin Laden. Even if Osama is dead, the international movement may continue. The War on Terror won't be won until Osama's ideology is buried once and for all.

Peter Brookes is a Heritage Foundation senior fellow. His book, "A Devil's Triangle: Terrorism, WMD and Rogue States," is just out.