A new data-recovery technique is set to trace suspicious financial transactions made shortly before the terrorist attacks in the US on September 11.

An unexplained surge in transactions was recorded prior to the attacks, leading to speculation that someone might have profited from previous knowledge of the terrorist plot by moving sums of money. But because the facilities of many financial companies processing the transactions were housed in New York's World Trade Center, it has, until now, been impossible to verify that suspicion.

Convar Systeme Deutschland is helping reconstruct data from hard-disk drives found in the ruins of the twin towers. While other data-recovery companies are involved in the effort, the company says it has a special edge: a laser-based scanning technology developed about two years ago.

"Using the technology it's possible to read the individual drive surfaces, and then create a virtual drive," said Peter Wagner, a spokesman for the company, a subsidiary of UK-based Convar Europe. "Our competitors mostly work with magnetic heads, which is a very tedious process, but also risky."

Because of the fine dust created by the explosions that destroyed the towers, which was driven at high pressure into devices, physically touching the drive surfaces can damage them, he said.

"Laser scanning is a good deal quicker, has a higher success rate, and is also cheaper," he added. Companies contracting with Convar pay between $20,000 and $30,000 per drive for the work.

When Convar discovers encryption keys on a drive, indicating a financial record, it saves the information and hands it over to its US clients, who are in turn co-operating with the Federal Bureau of Investigation (FBI), he said.

The company has completed processing 39 drives; another 42 have arrived, and a further 20 drives are expected in early January, Wagner said.

Convar's German facility, in the town of Pirmasens near the NATO air base Ramstein, is one of the few civilian data-recovery centres to be certified for military purposes as a "high security zone", the company said.