Jérôme Kerviel made trades totalling $78 billion that incurred $7 billion in losses, says Société Générale. (Société Générale via Getty Images)

Investigators at Société Générale said Friday they suspect a former futures trader had help as he tried to cover up unauthorized positions that led to billions in losses at the French bank.

In two long-awaited reports, the investigators said the French bank's management failures and culture of risk-taking were partly to blame for failing to uncover the alleged fraud, which led to a loss of almost five billion euros.

"The trader's hierarchy, constituting the first level of control, proved deficient in the supervision of his activities," said the board of directors in a statement to shareholders accompanying the reports.

It also said former trader Jérôme Kerviel's direct superior "lacked trading experience," and showed "an inappropriate degree of tolerance" for Kerviel's trading activity.

The findings came in two separate internal reports — one led by a committee of independent directors headed by former auto executive Jean-Martin Folz, the other by audit firm PriceWaterhouseCoopers.

The report from the directors said they had "discovered indications of internal collusion involving a trading assistant," who they declined to identify. They said they were unable to speak to the person because of an ongoing judicial probe, adding that it will be up to the court to confirm its suspicions.

However, they said they had uncovered an e-mail which suggested that the assistant must have known about the fake trades.

The assistant's complicity would have helped Kerviel avoid detection, the report said.

Previously, Société Générale had said it believed that Kerviel acted alone.

No signs of embezzlement: report

The internal report said it found that "neither JK's hierarchical superiors, nor his colleagues, were aware of the fraudulent mechanisms used or the size of his positions."

Kerviel says his superiors must have known what he was doing, but that they chose to look the other way when he was making money for the bank.

Investigators didn't find any signs of embezzlement by Kerviel, but said it appeared that he had sought to boost his results, and thus increase his bonuses.

The internal report said supervision of Kerviel was weak and management failed to react to a series of red flags

The report by PriceWaterhouseCoopers cited a culture of risk-taking at the bank as it grew its investment banking business. Trading limits were often surpassed, the report said.

Control systems were missing and procedures were lacking, that report said.

The bank's board said in a statement it approved the conclusions of the report and its recommendations.

Société Générale SA has said it is tightening computer security, reinforcing controls and taking more account of the possibility of fraud since the affair was uncovered.