After 10 months of stitching together evidence on the firm's demise, criminal investigators are concluding that chaos and porous risk controls at the firm, rather than fraud, allowed the money to disappear, according to people involved in the case.

The hurdles to building a criminal case were always high with MF Global, which filed for bankruptcy in October after a huge bet on European debt unnerved the market. But a lack of charges in the largest Wall Street blowup since 2008 is likely to fuel frustration with the government's struggle to charge financial executives. Just a few individuals — none of them top Wall Street players — have been prosecuted for the risky acts that led to recent failures and billions of dollars in losses.

In the most telling indication yet that the MF Global investigation is winding down, federal authorities are seeking to interview the former chief of the firm, Jon Corzine, next month, according to the people involved in the case. Authorities hope that Corzine, who is expected to accept the invitation, will shed light on the actions of other employees at MF Global.

Those developments indicate that federal prosecutors do not expect to file criminal charges against the former New Jersey governor. Corzine has not yet received assurances that he is free from scrutiny, but two rounds of interviews with former employees and a review of thousands of documents have left prosecutors without a case against him, say the people involved in the case who spoke on the condition of anonymity.

While the government's findings would remove the darkest cloud looming over Corzine — the threat of criminal charges — the former Goldman Sachs chief is not yet in the clear. A bankruptcy trustee on Wednesday joined customers' lawsuits against Corzine, and regulators are still considering civil enforcement actions, which could cost him millions of dollars or ban him from working on Wall Street.

Corzine, in a bid to rebuild his image and engage his passion for trading, is weighing whether to start a hedge fund, according to people with knowledge of his plans. He is currently trading with his family's wealth.

If he is successful as a hedge fund manager, it would be the latest career comeback for a man who was ousted from both the top seat at Goldman Sachs and the New Jersey governor's mansion.

A spokesman for Corzine declined to comment.

Even with the worst behind him, Corzine's reputation has suffered lasting damage.

After the collapse of the firm, which left farmers and other MF Global customers out millions of dollars, Corzine became another face of Wall Street recklessness. Lawmakers called him back to Washington, a humbling return to the town where he once served as a Democratic senator from New Jersey, to seek answers and to criticize him. With a criminal case unlikely to materialize, the anger over the collapse of MF Global is likely to grow.

Typically in white-collar cases, investigators start their interviews with lower-level employees and build up to the top executives of a firm. In July, when federal authorities first approached Corzine's lawyers, it was not clear whether he would agree to an interview. But the signs were good. In such cases, if prosecutors have damning information, they often file charges rather than extend an offer for a voluntary interview.