Last month, Blumont Group Ltd, Asiasons Capital Ltd and LionGold Corp Ltd - three firms interlinked by cross shareholdings and common officers - lost a combined market value of about S$8 billion ($6.4 billion) in just three days of trading.

The court case may shed light on the causes of the crash. Both the crash and huge run-ups in their share prices earlier in the year left many in the market mystified, prompting the Monetary Authority of Singapore and the stock exchange to launch an extensive review.

The lawsuit was filed in the High Court in London on November 20 by Quah Su Ling, who held stocks in all three companies and is the chief executive of investment firm IPCO International Ltd, the second-largest shareholder in Blumont. It is being brought against London-based Goldman Sachs International, a fully owned unit of Goldman.

Quah said that on October 2 Goldman demanded she pay back about S$61 million ($49 million) in loans in cash, giving her only 1.5 hours to do so, according to the filing which was seen by Reuters.

As Quah failed to make the repayment, Goldman issued a notice of default and immediately started to sell Quah's collateral, including shares in investment firm Asiasons, Blumont, a natural resources investment company, and gold miner LionGold, the filing says.

She also said that Goldman neglected to contact Hong Kong-based Vicario Investments Limited, which had agreed to buy 10 million shares each in LionGold and Blumont from her in cash, according to the filing.

"...the Defendant continued to sell the Claimant's LionGold and Blumont shares knowing full well that the continued sale of the said shares would depress the share prices and jeopardize the intended purchase by Vicario," the filing added.

Sophie Bullock, a spokeswoman for Goldman in London, declined to comment on the case. Quah, who is seeking unspecified damages, could not be reached for comment.

Blumont and Asiasons did not respond to requests for comment about Quah's case. LionGold declined to comment. All three companies have previously denied any wrongdoing in relation to the falls in their share prices.

Contact details for Vicario Investments could not be immediately obtained by Reuters.

The alleged action by Goldman came after Singapore Exchange Ltd on October 1 issued a particularly detailed query to Blumont, asking if its activities had justified an eightfold rise in its share price in the first nine months of the year. The query was one of several made to the three companies in September and early October about the rise in their share prices.

Over the next few days, the three stocks started to plummet, transforming them back into the penny stocks they had once been.

Three other individuals also received demands from Goldman Sachs to repay loans on October 2, including Wong Chin Yong, chief executive officer of Innopac Holdings Ltd, James Hong, executive director at Blumont and Ng Su Ling, a director at LionGold and at the time, also a director at Blumont, according to the court papers.

Hong told Reuters that he was also suing Goldman Sachs but declined to elaborate further. It was not clear if a suit had been filed.

Records from the High Court in London show Ng has filed a lawsuit against Goldman, though details were also not immediately available. Ng could not be reached for comment, while LionGold said that Ng's suit was a personal case and did not relate to the management of the company.

Goldman's Bullock declined to comment on Ng's lawsuit and possible legal action by Hong.

Wong and Innopac, a property and equity investment firm, did not immediately reply to requests for comment.

Some brokers in Singapore had put trading restrictions on the stocks during September due to concerns that their value was no longer matched by fundamentals.

The Singapore Exchange queried Asiasons and Blumont twice and LionGold once about their share prices in the weeks leading up to the crash, but did not put in place trading curbs until after the stocks started to fall.

The exchange later came under fire for lifting those trading curbs before the companies could issue clarifications about their stock moves. It has said that it deployed a series of tools to restore stability in the market when the stocks began to fall and that it uses separate measures to investigate possible wrongdoing. ($1 = 1.2543 Singapore dollars)

(Additional reporting by Rachel Armstrong in SINGAPORE and Kirstin Ridley in LONDON; Editing by Edwina Gibbs)

By Rujun Shen