GARY Foster toiled away as a mid-level accountant in Citigroup's Long Island City back office, collecting about $US100,000 in salary last year.

But federal prosecutors claim Foster gave himself a bonus fit for a star investment banker by embezzling more than $US19.2 million ($A18.4 million) from Citi before its auditors picked up on the scheme.

Foster, a 35-year-old former assistant vice-president in Citi's internal treasury finance department, was arrested by Federal Bureau of Investigation agents at John F. Kennedy International Airport on Sunday morning after returning from a trip to Europe and Asia.


On Monday afternoon, he pleaded not guilty to charges of bank fraud at a court hearing in Brooklyn.

Foster, who is divorced and has two children, had been enjoying the high life. He owned six properties, including an apartment in mid-town Manhattan, two luxury apartments in Jersey City, and homes valued at $US3 million and $US1.35 million in New Jersey, according to a law enforcement official.

He also owned a Maserati and a BMW, with a Ferrari on order, the official said.

Foster's lawyer, Isabelle Kirshner, said she had spoken only briefly with her client and had just started to review the allegations.

''We will investigate the matter thoroughly,'' she said.

The fraud charges are the latest effort by the US Justice Department to crack down on white-collar crime at a time when the agency is under increasing pressure to hold Wall Street bankers accountable. This case is against a relatively junior Citigroup executive and appears to have little to do with the financial crisis.

Still, it is yet another embarrassment for a bank that once made its entire workforce take an ethics pledge and uses ''responsible finance'' as a corporate slogan.

It also raises new questions about Citi's internal controls, nearly two years after regulators forced it to strengthen its risk management and compliance practices upon losing tens of billions of dollars during the financial crisis.

Earlier this month, the bank came under fire from politicians after taking more than a month to disclose that hackers stole data from more 360,000 Citi credit card accounts.

In this case, it took nearly a year after the claimed embezzlement began before Citigroup's internal auditors uncovered that millions of dollars were missing.

To conceal some of the transactions, the complaint contended that Foster used a false contract or deal number to be placed in the reference line of the wire transfer.

Citigroup detected the fraud several weeks ago during an internal audit of the treasury department, where Foster worked.

The bank said it immediately contacted law enforcement officers after discovering the suspicious transactions, and had put in additional safeguards and internal controls.

''We are outraged by the actions of this former employee,'' said Shannon Bell, a Citigroup spokeswoman. If convicted, Foster faces up to 30 years in jail