Fairfield Greenwich Group, the hedge fund that has potentially lost $7.5 billion it invested with Bernard Madoff, has been sued by some of its own investors alleging negligence.

In a class action led by Pasha and Julia Anwar, Fairfield’s fund managers are accused of failing to manage the investors’ money with due diligence, leading to “avoidable losses”. The investors also attack Fairfield for reaping “unjust” fees.

The lawsuit, filed in the Supreme Court in the State of New York, comes as hedge funds, charities, universities and individuals scramble to lay claim to the carcass of Mr Madoff’s liquidated firm, and seize back some of the estimated $50 billion worth of losses incurred by the alleged Ponzi scheme.

At the same time, the role of feeder funds that supplied new capital to Mr Madoff’s scam was yesterday again called into question as lawyers began to look into how diligently parent companies oversaw the activities of their hedge funds.

Massachusetts Mutual Life, the insurance group, owns Tremont, a hedge fund that lost $3.3 billion in Mr Madoff’s Ponzi scheme. Tremont is one of the biggest casualties so far in the Madoff affair. The insurer issued a statement last week claiming: “MassMutual has very limited exposure to the alleged fraud by Bernard Madoff.”

Trevor Allan, general manager of the Shareholders Foundation, a non-profit body that informs investors of securities class actions, said that he expected savers who lost money in the scam to pursue the feeder funds and their parent companies.

However, Irwin Latner, head of the hedge fund practice at the law firm Herrick, Feinstein, said that MassMutual could argue that Tremont, a wholly owned subsidiary of the insurer, was managed independently.

MassMutual declined to comment.

Separately, regulators refused to be drawn on the identity of a third party who was reported to have been tipped off by the financier about the Ponzi scheme. Mr Madoff is believed to have told his two sons, Mark and Andrew, who both worked for their father, that he planned to turn himself in on December 9. The sons reported their father to the FBI.

According to Theodore Cacioppi, an FBI special agent, Mr Madoff first confessed to an individual known as “Employee No 3”.Regulators would not be drawn on whether Employee No 3 was Mr Madoff’s brother, Peter, who was head of compliance at the firm. Peter Madoff’s lawyer failed to return calls.

— Kingate Global, a feeder fund that provided new capital to Bernard Madoff, is believed to have told its clients that it would not check the veracity of any financial statements made by Mr Madoff. According to reports, despite the warnings, its own clients still opted to invest $2.75 billion with Mr Madoff. Kingate Global was unavailable for comment last night.

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