Refco's collapse was the fourth-biggest US bankruptcy case.Phillip Bennett was speaking in court after pleading guilty to conspiracy and fraud charges that could seem him given a prison sentence of up to 315 years.
Refco went bust in 2005. It has since come out of bankruptcy protection.
Prosecutors said Bennett had prevented auditors and investors discovering the losses the firm and customers suffered.
The charges included conspiracy to commit securities fraud, wire fraud, bank fraud, money laundering and making false filings to the Securities and Exchange Commission.
The US government said that Refco and its customers had built up heavy losses in the mid-1990s when the company was privately owned with Bennett in charge.
The firm went public in 2005 but filed for bankruptcy weeks later after the $430m black hole in its books was revealed.
Bennett, who is from the UK, said he took "full responsibility" for his actions and apologised to those "harmed" by his conduct. His lawyer added: "He has candidly acknowledged his involvement in the matter. He was forthcoming and candid and wants to put this matter behind him." Bennett will be sentenced in May, with a maximum term of up to 315 years. US District Judge Naomi Reice Buchwald said a lengthy term would not be unusual for someone "facing sentencing in the post-Enron era