Federal authorities investigating the demise of MF Global think that the firm began improperly moving customer money to a middleman Oct. 27, according to people briefed on the matter.

The transfers, which indicate the brokerage firm misused client funds earlier than previously believed, represent a new line of inquiry in the hunt for more than $1 billion in missing money.

In MF Global's last days, the brokerage house was frantically winding down trades to shore up its balance sheet and stave off bankruptcy. Investigators are examining whether the firm — as part of that effort — began moving client funds to the Depository Trust & Clearing Corp., a financial intermediary responsible for closing out some of MF Global's transactions, these people say.

The new details bolster claims that MF Global was careless with customer money, regardless of the company's intentions. Authorities previously found that MF Global had used roughly $200 million of client funds to replenish an overdrawn account at JPMorgan Chase in London on Oct. 28, the last business day before the firm filed for bankruptcy.

Now, investigators are also looking at billions of dollars of transfers from MF Global to the Depository Trust, a fraction of which is believed to be customer funds. People briefed on the matter say the middleman passed some of the money to banks and other firms that traded with MF Global, which was once run by Jon Corzine, the former governor of New Jersey.

In addition, federal authorities are reviewing whether MF Global used customer money to pay the clearing corporation as part of a margin call. Financial intermediaries routinely require extra collateral when firms run into trouble. A different clearinghouse in London forced MF Global to pay roughly $300 million to back some of its bond holdings during its last week.

It is unclear how much customer money was transferred to the Depository Trust and whether officials at MF Global knew they were using client funds. Haphazard record-keeping and the flood of transactions in its final days might have concealed whether MF Global was deploying the customer cash for firm needs.

A spokesman for the clearing corporation declined to comment.

Kent Jarrell, a spokesman for the trustee overseeing the liquidation of MF Global's brokerage unit, said that the trustee "has not made a determination about customer cash that went through" Depository Trust.

"We will make a legal determination about whether customer money can be recovered," Jarrell said. If it can be recovered, "we will use all legal avenues to do so," he added.

As MF Global transferred funds to the clearing corporation, regulators started to raise concerns about the customer money after a routine inquiry. In the firm's final week, senior officials at the Commodity Futures Trading Commission (CFTC) asked MF Global employees about the money. In response, the firm provided a document that highlighted specific MF Global units, according to a person briefed on the matter.

But one of the units, MF Securities, was not listed on the firm's broader organizational chart, the person said. That discrepancy raised red flags among regulators that the firm might have been misusing customer money.

A person close to MF Global says that the firm's broker-dealer unit used to be called MF Securities, and people in the company often referred to it by that name. Even so, regulators at the CFTC pushed for assurances that the money was safe. MF Global asked for more time.

Three days later on Oct. 30, MF Global alerted federal authorities to the shortfall.

Since then, regulators and the trustee, James Giddens, have been searching for the money. The shortfall is now estimated at $700 million to $1.2 billion. The situation has left customers like farmers and hedge funds without a third of the money in their MF Global accounts.