Intelligence agencies that have succeeded in thwarting many of al-Qaeda’s plans for spectacular attacks are struggling to combat the terror network’s strategy of encouraging followers to keep to themselves, use off-the-shelf weapons and strike when they see an opportunity.

In recent weeks at the Boston Marathon; in the streets of London; and in the shadow of one of Paris’ most recognisable monuments, young men allegedly carried out attacks with little help, using inexpensive, widely available knives and explosives from everyday ingredients. In each of the attacks, suspects had previously been flagged to law enforcement and deemed not to be a priority.

A tough debate is raging within the intelligence community, previously focused on searching for al-Qaeda cells on how to assess red flags without violating basic liberties.

Confronting an overwhelming sea of mostly harmless individuals who act suspiciously, authorities are still struggling with questions about how and how much to keep tabs on people who spout jehadist rhetoric online or buy material that could be used to make explosives or something innocuous.

A French government report last week recommended a radical new approach in light of the 2012 terror in which a French-born radical Muslim attacked French paratroopers and a Jewish school in Toulouse, killing seven people. It called for an overhaul of the country’s intelligence networks to combat the rising threat of militants working alone outside established terror networks.

One of the report’s advisers, academic Mathieu Guidere, said last week’s attack showed that intelligence services haven’t learned their lesson.

British, French and American officials are re-examining whether opportunities might have been lost in the run-up to the recent attacks.

Analysts say rapidly evolving technology and better recruitment of intelligence officers should allow authorities to better track patterns of dangerous behaviour.

For its part, the U.S. government has emphasised that local communities are most likely to spot unusual or suspicious behaviour, and has encouraged more outreach to communities that might be vulnerable to radicalisation. The federal government has led a nationwide suspicious activity reporting campaign and trained local police to identify potential terror-related activities.

Clearly, al-Qaeda has placed a big bet on the lone-wolf model as its own best hope of success.

The first issue of al-Qaeda’s in-house magazine Inspire , in 2010, called on recruits to avoid plotting with others, to strike near home and to use whatever weapons were at hand. In all three recent attacks allegedly by young radical Muslims in the U.S., Britain and France that advice seemed to be followed nearly to the letter.

The pattern of suspects in terrorist attacks having been investigated and discarded as serious threats is certainly nothing new.

After the 2005 suicide bombings in London that killed 52 people during morning rush hour, a parliamentary report found that at least two of the men had been on the periphery of other surveillance and investigative operations.

“Some significant changes were put into place after the July 7 suicide bombings,” said a British security official who refused to elaborate and spoke only on condition of anonymity because he was not authorised to speak about operational issues.

“And like the 2005 attacks, we are again looking to see if anything different could have been done.” — AP