CHICAGO, Aug 9 (Reuters) - A ruling in the case of failed futures brokerage Sentinel Management Group could make it more difficult for customers to recoup money lost in the much larger collapse of MF Global, according to Sentinel's bankruptcy trustee.

A federal appeals court on Thursday upheld a ruling that puts Bank of New York Mellon ahead of former customers of Sentinel in the line of those seeking the return of money lost in the 2007 failure of the suburban Chicago-based futures broker.

The appeals court affirmed an earlier district court ruling that the bank had a "secured position" on a $312 million loan it gave to Sentinel, which turned out to have been secured by customer money.

Futures brokers are required to keep customers' funds in dedicated accounts to protect them from being used for anything other than client business.

However, Thursday's ruling suggests that brokerages can use customer funds to pay off other creditors, Sentinel trustee Fred Grede told Reuters.

"I don't think that's what the Commodity Futures Trading Commission had in mind" with its requirement that brokers keep customer money separate from their own, he said.

"It does not bode well for the protection of customer funds."

Worse, Grede said, is that the ruling suggests that a brokerage that allows customer money to be mixed with its own is not necessarily committing fraud.

That may raise the bar for proving that MF Global Holdings Ltd, under then-CEO Jon Corzine, misused customer funds as it scrambled to meet margin calls to back bets on European debt in the brokerage's final days. A $1.6 billion customer shortfall remains.

Corzine has said he did not know about the transfer of any customer money.

"I'm sure Mr. Corzine's attorneys will get ahold of this ruling and use it for all it's worth," Grede said.

A lawyer for Corzine, who has not been charged with any crimes, did not immediately respond to a request for comment.

CORZINE MAY STILL FACE SCRUTINY

CME Group Executive Chairman Terrence Duffy, whose firm was MF Global's frontline regulator, has said MF Global made unlawful transfers of customer money to plug its own liquidity needs.

James Koutoulas, head of the Commodity Customer Coalition, which has been an advocate for MF Global clients, said Corzine could still face scrutiny for the transfers.

The Sentinel ruling is "not an end-all-be-all acquittal for Corzine," he said.

Sentinel allegedly pledged hundreds of millions of dollars in customer assets to secure an overnight loan at Bank of New York Mellon, leaving the bank in a secured position but Sentinel's customers out millions.

Customer funds were allegedly moved from the protected accounts to other accounts so they could be used as collateral for loans to Sentinel's own trading operations.

The appeals court said that "perhaps the bank should have known that Sentinel violated segregation requirements" but agreed with the district court's earlier ruling that "such a lack of care does not rise to the level of the egregious misconduct" needed to reprioritize a claim.

"That Sentinel failed to keep client funds properly segregated is not, on its own, sufficient to rule as a matter of law that Sentinel acted 'with actual intent to hinder, delay, or defraud' its customers," U.S. Circuit Judge John D. Tinder wrote in the ruling.

The decision was a blow for Grede, who had sought to strip Bank of New York Mellon of its secured position.

Sentinel, whose customers are missing about $600 million, largely managed money for other futures brokers, delivering outsized returns that, Grede says, were juiced up by improperly using customer money to secure loans that went to fund risky trades.

The scheme unraveled when the credit crisis hit in the summer of 2007. 

(Reporting by Tom Polansek and Ann Saphir; Additional reporting by Jonathan Stempel)

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