Police say former UBS trader Kweku Adoboli made his reckless trades difficult to detect.
Detective Chief Inspector Perry Stokes, who led the investigation said the 32-year-old, was one of the most sophisticated fraudsters he had seen.
When you've got a rogue employee in a position of trust it's very difficult when they are intent on breaking the rules to identify what they are doing. As an organisation you put your trust in your employee and if you get a rogue it's very difficult to detect... This isn't someone who has made a mistake in the course of his business, this is someone who has chosen the path that they have gone down. If you're a bad trader, you're a bad trader. He has gone down a different path and he has lied to colleagues.
The trial of a City trader from east London accused of losing £1.4 billion while working for Swiss Bank UBS is due to begin.
Kweku Adoboli will appear at Southwark Crown Court in London this morning to face two counts of fraud and two counts of false accounting.
The prosecution case is not expected to open until later in the week.
Adoboli, who is 32 and from Clark Street, Whitechapel, is accused of losing the money in Britain's biggest alleged banking fraud.
He worked for UBS's global synthetic equities division, buying and selling exchange traded funds, which track different types of stocks, bonds or commodities such as metals.
Adoboli is accused of dishonestly using his position to try to make a personal gain, and causing UBS losses or exposing the bank to the risk of loss.It is alleged he lost a total of 2.25 billion US dollars, and charges relate to the period between October 2008 and last September.