Investigators say Kerviel's bosses missed more than 1,000 faked trades; a huge jump in his earnings in 2007; questions about his trades from the Eurex exchange; unusually high levels of cash flow, accounting anomalies, and high brokerage expenses; Kerviel's failure to take vacation; and his breach of the desk's market risk limit on one position.
"The trader's hierarchy, constituting the first level of control, proved deficient in the supervision of his activities," Societe Generale's board of directors said in a seven-page statement to shareholders accompanying the reports.
The reports said Kerviel's direct superior "lacked trading experience" and showed "an inappropriate degree of tolerance" about his trades.
The bank did not name the superior, who they said they have been unable to question because he no longer works for the company.
The reports criticised the manager of the company's Delta One trading desk, who they said was aware of the lack of experience of Kerviel's manager, and "deficiencies in the monitoring of risks by the desk in general".
One report was led by a committee of three board directors, the other by audit firm PriceWaterhouseCoopers.
They were published in the run-up to Tuesday's annual shareholder meeting.
The report by the directors said that they had "discovered indications of internal collusion involving a trading assistant", whom they declined to identify.
They said they were unable to speak to the assistant because of an ongoing judicial probe, explaining 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 being uncovered, the directors' report said.
Previously, Societe Generale had said it believed that Kerviel acted alone.
But while he allegedly had help from a junior colleague, the internal report 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.
"We notice that while protecting the superiors of Jerome Kerviel, the Societe Generale has found a new scapegoat - who just happens to be a 23-year-old assistant," Guillaume Selnet, a lawyer for Kerviel, said.
He noted that the directors' report was prepared by the bank's own services and insisted that Societe Generale's version of events keeps changing.
The bank issued a preliminary investigation into the scandal in February. "My feeling is that - we are now on the second report - by the third report it's going to be the fault of the cleaning ladies," Selnet said.
"Each time it goes down (the corporate hierarchy), instead of up."