Jill Sommers, who is heading the Commodity Futures Trading Commission's review of MF Global, said regulators "are far enough along the trail" that they know where the money went.
"Now it's just finding out which ones of those transactions are legitimate and which ones of them are illegitimate," Sommers said.
The CFTC and the trustee liquidating the firm are under intense pressure from lawmakers and customers to provide answers about what happened to hundreds of millions of dollars in customer money that went missing as the firm collapsed.
MF Global officials, including former Chief Executive Jon Corzine, have told lawmakers they simply do not know where the money is, and deny authorizing any misuse of customer money.
"We certainly don't want to lead anyone to believe we don't know what happened. We do know, and we see where all the transactions went," said Sommers, a Republican commissioner, in an interview on Wednesday.