The man at the centre of the scandal was the key naptha trader of Mitsui back in 2006. Mitsui accounted for about half the trades of naptha trading in Singapore.

Naptha is a petroleum product that is used in the petrochemical industry. It is not publicly traded on exchanges like the Singapore Exchange but is an 'over-the-counter' product.

Around 2005 and 2006, the spot rent prices of naptha started to be lower than the forward or expected future prices. This affected Mitsui's portfolio which had expected the opposite.

As the losses rose, Yamazaki falsified the prices of the naptha products in a daily spreadsheet which was used by a another department to prepare the estimated losses and gains on a daily basis. This department would send the report to head office in Tokyo. Once the limit on losses is breached, traders will have to close their positions or cut their losses.

As the losses ballooned to US$71 million in November 2006, Yamazaki believed that a sudden closing-off of the positions would not be the best for the Singapore office.

In his mitigation plea in the Subordinate Courts on Friday, his lawyer Senior Counsel Sant Singh said that the trader believed that the prices of naptha would recover.

The losses were eventually discovered in November 2006 after an internal investigation.

Yamazaki was charged last year with 109 charges relating to the affair. He admitted to 10 charges on Friday, with the rest being taken into consideration. Mitsui has now closed down the Singapore office.

Yamazaki, married and has two young children, faces a jail term of up to seven years and/or a fine. He will be sentenced on Feb 25.