But inside the offices of SAC's Stamford, Conn., headquarters, and at Midtown Manhattan law firms, Mr. Cohen's employees and lawyers are working hard to contain the fallout from the investigation.
His executives have offered financial incentives to Mr. Cohen's staff members to stay with SAC. Marketing officers are trying to persuade investors to keep their money at the fund. And defense lawyers are working furiously to persuade federal securities regulators not to file a civil fraud lawsuit against the firm.
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"This has always been a stressful place to work," said an SAC employee who requested anonymity because he was unauthorized to speak publicly about the fund. "Now it's just more stressful."
Neither SAC nor Mr. Cohen has been accused of any wrongdoing.
The main question now looming over the firm is whether its clients will stand by the fund, or its legal and regulatory problems will cause investors to head for the exits. Under the firm's rules, SAC clients have until Feb. 15 to ask for their money back, and then cannot make another so-called redemption request for another three months.
Mr. Cohen's fund was dealt a blow last week when a Citigroup unit that manages money for wealthy families disclosed that it was withdrawing its $187 million investment. The move by the bank was the most prominent client departure since November, when the multiyear investigation into SAC's trading practices entered a more serious phase.
Citigroup's withdrawal represents a tiny percentage of SAC's $14 billion in assets under management. The fund has said it expects total investor redemptions for the first quarter of up to $1 billion, a number that an SAC spokesman has said will not adversely affect its business.
SAC is largely insulated from the potentially devastating effects that client defections can have on a hedge fund in part because of Mr. Cohen's extraordinary wealth. Unlike other hedge fund managers who rely almost entirely on outside investors, Mr. Cohen has the comfort of knowing that about $8 billion of SAC's fund belongs to him and his employees.
Still, the Citigroup decision stung, say people close to SAC's business, because of the longstanding and lucrative relationship between the bank and the fund. Another concern, said these people, is that the move could influence other large SAC investors currently weighing whether to keep their money at the fund.
For Citigroup, its withdrawal of money from SAC carries substantial business risk. The bank has a vast relationship with SAC, earning revenue by providing the fund with financing and trading services.
SAC could exact retribution on Citigroup by terminating, or at least scaling back, its broader relationship with the bank. An SAC spokesman declined to comment.
Citigroup's move came two months after federal authorities arrested Mathew Martoma, a former SAC portfolio manager, in what they described as the most lucrative insider trading case ever uncovered. The Martoma indictment represented the first time that the government had brought charges stemming from a trade in which Mr. Cohen had been involved. The Securities and Exchange Commission has warned Mr. Cohen that it might file a civil fraud action against SAC related to the case.
In addition to Mr. Martoma, at least seven former SAC employees have been tied to insider trading while at the fund. Three have pleaded guilty to criminal charges.
Citigroup issued a statement that its decision "should not be construed as a statement on the merits of any outstanding legal proceedings or potential regulatory action." But the bank specifically cited the Martoma case, explaining that "in the event these legal and regulatory matters are resolved favorably for Mr. Martoma and SAC, Citi Private Bank expects to reconsider admission of SAC's funds to its hedge fund platform."
Mr. Martoma has pleaded not guilty and rejected requests by federal agents to cooperate against his former boss. Mr. Cohen has told his employees and clients that he is confident that he has acted appropriately at all times.
Yet the heightened government scrutiny has caused skittishness among SAC's top ranks, forcing the fund to lavish even richer financial incentives on a group of employees that is already among the most highly compensated in the hedge fund industry.
This month, SAC told its stable of portfolio managers that it would increase year-end bonuses by three percentage points. SAC portfolio managers — the fund's most senior traders, given the authority to make their own investment decisions and also feed Mr. Cohen their best ideas — are paid, on average, 20 percent of the profits they generate for the fund.
"The program is intended to retain our most valuable resource, our investment professionals," said Jonathan Gasthalter, the SAC spokesman.
Another valuable resource is SAC's outside investors, which account for about $6 billion, or 40 percent, of the fund's assets. That money accounts for hundreds of millions of dollars in fees, which SAC uses to finance one of the world's largest and most sophisticated hedge fund operations, with more than 1,000 employees and 125 teams of traders and analysts. Its operation is also one of the most successful, posting average annualized returns of about 30 percent since 1992.
Those results have in the past kept SAC's customers satisfied, but the government scrutiny has made many of them uneasy. The firm's marketing team has reached out to the fund's investors to address their concerns and reassure them that the insider trading inquiry will not affect its performance.
Despite those efforts, several investors in addition to Citigroup, including Titan Advisors and a unit of Societe Generale, have notified SAC that they are withdrawing money. Other clients, like Chapwood Investments and SkyBridge Capital, have said they will continue to invest with the fund.
SAC executives continued the charm offensive with major clients on Sunday, holding an annual golf outing in Palm Beach on the eve of a hedge fund conference at the Breakers sponsored by Morgan Stanley. The conference — a matchmaking event that connects top managers with the world's richest investors — is considered an important stop on the hedge fund money-raising circuit.
Since Morgan Stanley does not invite the news media to its conference, there is not expected to be the same paparazzi-like reports on Mr. Cohen that emerged last week from Davos. Bloomberg News filed a dispatch that Mr. Cohen sat in on a panel discussion on data security called "The Digital Infrastructure Context." And Henry Blodget, the editor of the financial Web site Business Insider, wrote a Twitter post on a sighting of Mr. Cohen.
"Steve Cohen was hanging in Davos lounge yesterday," he wrote. "Didn't look worried."