Curbing cash payments for dangerous knives and chemicals could make potential terrorists easier to trace, a report said.
An analysis by the Royal United Services Institute said solo terrorists leave financial footprints despite their generally unsophisticated schemes.
But they are harder to find if the extremists use cash to pay for items such as ornamental knives, or chemicals that can be used in explosive devices but on their own might be innocuous.
In one example, the attacker who carried out the 2016 lorry rampage in Nice was said to have rented the vehicle with cash after selling his own car.
EU leaders could consider stopping cash payments or requiring customers to prove their identity before buying dangerous items, the Rusi report said.
“The private sector and EU agencies have better prospects of tracing suspicious activity where cash is not used,” it said.
“The European Commission should therefore review the potential benefits of limiting cash payments (or requiring customer identification and verification) in the purchase of a small number of high-risk items.”
Europol’s latest annual report on terrorism said lone actors who did not taking orders from larger terrorist groups were the greatest threat to EU countries.
It said that extremist plots which relied on international funding from sophisticated terrorist networks went into decline after 9/11.
By contrast, solo terrorists had limited financial requirements because they had no infrastructure to maintain.
Nonetheless, the Rusi report said their financial activity was “more complicated than is commonly assumed” and could draw attention.
Terrorists' suspect moves in run-up to attacks
Some attackers engaged in “burst activity” in the final days before their atrocities, for example by withdrawing large amounts of cash or making major financial transfers to associates.
The 2016 Nice attacker was reportedly denied service several times by ATMs after making four major cash withdrawals.
Anton Lundin Pettersson, who purchased Nazi memorabilia before attacking a school in Sweden in 2015, is said to have withdrawn all his money from the bank and left the remainder on his brother's kitchen table.
Such transactions may not be directly related to the attack but can indicate a changing pattern of behaviour, the Rusi report said.
In addition, attackers do not necessarily rely on their own resources even when they could do so.
The London Bridge terrorists of June 2017 bought their weapons from a supermarket weeks earlier rather than using knives they already had at home, an inquest was told.
Other extremists are thought to fund themselves through petty crime such as shoplifting and extortion.
“Self-activating terrorists can and do draw attention to themselves through their financial and procurement activity, and the more ambitious their plans, the more attention they draw,” the report said.
Among its recommendations, the report said Europol should work with national intelligence agencies to study the finances of previous terrorists.
This would allow authorities to identify how terrorists behave typically in the prelude to an attack, it said.
Such information could then be shared with national authorities and financial institutions so that suspicious behaviour could be spotted in time.
