Last October, Goldman Sachs (GS  ) went before a U.S. court and admitted that it was guilty of taking part in a crime for the first time since it was founded more than one hundred and fifty years ago. That crime also happened to be one of the largest cases of government theft in history, involving more than $4 billion being stolen from a Malaysian sovereign wealth fund.

The 1Malaysia Development Berhad (1MDB) sovereign wealth fund was plundered by bank and government officials to pay for mountains of luxury goods, including paintings by both Monet and van Gogh, high-end jewelry, and real estate in London, Beverly Hills, Manhattan, and beyond.

Now, Goldman Sachs is in court once again, this time in a case against a former Goldman employee, Roger Ng, who is accused of taking part in the scheme to carry out the fraud. The key witness against Ng is another Goldman employee, Tim Leissner, a man who had admittedly "lied a lot". Leissner has already pleaded guilty to fraud charges and was Ng's boss during the scheme.

Leissner was Goldman's biggest player in Asia for years, and his ten days on the witness stand during Ng's trial have been explosive.

Ng's lawyers already knew Leissner was an admitted liar before he took the stand, and their questioning went over Leissner's long history of misleading people, including all three of his wives. Leissner admitted to providing one of his wives with a false divorce decree in order to convince her to marry him; this was actually the second time Leissner entered a bigamous marriage.

When asked if he was good at lying, Leissner replied, "I don't think so."

The other key player in the case is financier Jho Low, who is currently living as a fugitive. Lo allegedly served as the architect of the entire scheme. Leissner says that Ng was Lo's primary contact with Goldman and that Ng set up many of the meetings, including the meeting during which Lo pointed out all of the Malaysian officials they would need to bribe.

While Leissner says he made more than $80 million on the scheme, Ng made closer to $35 million. However, Ng's attorneys claim that the money received was a legitimate debt repayment for money Ng's wife had loaned one of Leissner's wives.

Ng's attorneys are attempting to prove that Leissner is falsely implicating Ng in the scheme in order to gain a lighter sentence for his own admitted crimes. While Ng spent six months in jail in Malaysia for his alleged involvement in the bribery plan, Leissner has avoided any jail time by cooperating with prosecutors.

In support of Ng's narrative, Leissner admitted on the stand that he was the one who oversaw the payment of most of the bribes. He also acknowledged having a close relationship with Lo.

Leissner's credibility may also be undermined by his initial resistance to giving law enforcement all the facts. Along with claiming at one point that a Morgan Stanley (MS  ) banker was also involved in the scheme, Leissner also held back information about meetings with Lo.

The fact that Leissner has repeatedly been characterized as a master con man, including by bank officials, may lend credence to the story.

However, experts in legal ethics say that Leissner's history of lying may not counteract his testimony if prosecutors can convince the jury that Leissner has had a "come-to-Jesus moment".

On the other hand, Ng could appeal a conviction if one is brought against him thanks to the government's behavior in this case. Recently, the trial was put on pause for several days so that Ng's attorneys could review tens of thousands of Leissner's documents that weren't provided until after the trial had already begun, a delay that prosecutors called "inexcusable".