Riedel is a hard-line conservative for whom jihadists are an existential threat to the West. Yet al-Qaida has been unable to replicate the horrors of Sept. 11, 2011.
The last major attack in Europe was the multiple bombings of London's transport system July 7, 2005, in which 54 people and four suicide bombers people were killed.
But then al-Qaida is no longer the highly centralized network it was in 2001.
Its founder and mastermind, Osama bin Laden, was killed by U.S. Navy SEALs in Pakistan May 2, 2011.
Dozens of his top- and mid-level commanders have been killed, mainly in U.S. drone strikes, decapitating the leadership of al-Qaida Central.
These days, the threat is more diffuse, coming from regional affiliates which run their own wars. The threat to the West is largely directed at its interests in regions far distant from the United States or Europe.
The jihadist storming of Algeria's In Amenas desert gas complex in January, apparently in retaliation for France's military push against jihadists in Mali, is a case in point.
So although the current surge of jihadist operations aren't a direct threat to Western civilization, they still cause deep concern among the West's intelligence services.
The mushrooming jihadist influence in Syria's civil war, now in its third year, threatens to destabilize the entire Middle East and ignite new sectarian conflicts in Lebanon, Jordan and Iraq.
Meantime, the maelstrom of turmoil triggered by the pro-democracy uprisings of the so-called Arab Spring that began in January 2011 has opened immense opportunities for the jihadists.
They were originally thought to have been marginalized by these revolutions, but they've exploited the chaos and strengthened their power.
The assassination of bin Laden "signaled a watershed in the West's long struggle with jihadism," the Financial Times observed.
But nearly two years on, "unease has returned and a new chapter in the battle against Islamic extremism appears to be underway ... U.S. and European governments have a right to be worried.
"Now the threat is more widely scattered and therefore more complex."
British Prime Minister David Cameron warned after the In Amenas slaughter, "We face a large and existential terrorist threat from a group of extremists based in different parts of the world who want to do the biggest possible amount of damage to our interests and way of life."
Echoes of George W. Bush in 2001 but, as al-Qaida expert Jason Burke observed, "A gas refinery in southern Algeria is not the Pentagon."
That may be so. But al-Qaida is attracting increasing numbers of Western Muslims and converts, particularly in Syria, just as the war in Iraq did a few years ago.
The International Center for the Study of Radicalization at King's College, London, concluded a yearlong survey of the Syrian conflict by noting, "We can say with certainty ... that hundreds of Europeans have joined the fight in Syria."
And here things get more complex, because there's a school of thought that Saudi Arabia and the other Arab monarchies are supporting the secondary uprisings in Egypt and Tunisia because they don't want democratic Muslim governments to succeed lest they threaten the future of their own absolute regimes.
Nigel Inkster, a former senior official with Britain's Secret Intelligence Service, observed: "When al-Qaida was largely holed up in the badlands of Pakistan and the tribal areas, the U.S. had the capability to deal with them in a much more focused way through drone attacks.
"But now we have a far more disaggregated threat that no one country has the capability to tackle."
Riedel says of al Qaida 3.0: "It's an adaptive organization and it has exploited the chaos and turmoil of revolutionary change to create operational bases and new strongholds ..."
It's "a complex and decentralized enemy that requires strategies tailored to each franchise. There's no one answer to each challenge. There's no 'strategic defeat' of al-Qaida in sight."