Sheikh Omar Bakri Muhammad is the leader of one of the most controversial Islamist groups in the U.K., Al Muhajiroun (which means "the emigrants" in Arabic). He attracted global media scrutiny on the first anniversary of 9/11 by staging a meeting entitled "A Towering Day in History," and unveiled a poster that depicted the second airplane advancing toward the World Trade Center. This month in Britain, Scotland Yard officials said they were investigating Sheikh Omar on suspicion of his support for "global jihad," including inciting Muslim youth to join the insurgency in Iraq. Omar, a Syrian, resides in Britain, which...