The accountant who uncovered alleged "rogue trades" by UBS trader Kweku Adoboli told a London court on Wednesday of the panic which swept through the Swiss bank as the defendant's story unravelled.
Ex-UBS accountant William Steward said at Adoboli's trial that he had asked the London-based trader why he had built up a hole in the accounts of over $2 billion by September 14 last year.
Steward told Southwark Crown Court that he informed the 32-year-old in a phone call that the bank had a "problem" if the counter-parties did not pay up the money owed.
He also warned Adoboli that "everyone (at the bank) was getting very excited".
The trades were causing a "great deal of anxiety" in the back office, the part of the bank which ensures that traders' books balance, he said.
In fact, the court heard, there never was a counter-party as the trades were fictitious.
Steward called Adoboli, the Ghanaian-born son of a former UN official, on September 14 to challenge why his explanations did not match the accounts, only to be told he had gone to a doctor's appointment.
The court was then told Adoboli sent an email to Steward admitting that the "hedged" deals were in fact fake.
According to Steward, the bank's automatic warning system had failed to flag up the exposure to its credit risk management department.
The accountant explained that the bank's London finance controller was "very concerned" when told about the exposure shortly before Adoboli sent his "bombshell" email admitting the trades.
The trial has heard that Adoboli caused "chaos and disaster" at Switzerland's largest bank when he "gambled away" $2.3 billion (1.75 billion euros) in trades at its London offices.
Adoboli denies two charges of fraud and two of false accounting between 2008 and September last year.