Madoff insists he acted alone
With disgraced US financier Bernard Madoff now behind bars, attention has turned to whether others were involved in his estimated $50bn (£35bn) fraud.
While Madoff insists he acted alone, prosecutor Lev Dassin said he was investigating if others had joined in the crime.
Investigators are also continuing work to see how much of the stolen funds can be recovered.
Madoff has been remanded in jail ahead of his sentencing in June.
This has seen him swap his wife's luxury Manhattan apartment for a small cell in New York's Metropolitan Correctional Centre, just a few miles away.
No plea deal
"We are continuing to investigate the fraud and will bring additional charges against anyone, including Mr Madoff, as warranted," said Mr Dassin.
He also rejected speculation that Madoff had agreed to plead guilty in exchange for leniency to help any others who may have been involved in the crime. "There is no agreement whatsoever," he said.
Madoff told his Thursday court hearing that his family members, and other colleagues, had only ever worked in parts of his business - Bernard L Madoff Investment Securities - that were "legitimate, profitable and successful".
Some of Madoff's thousands of victims have said they were angry that Madoff had been allowed to plead guilty, as this means he will avoid a full jury trial.
The victims had hoped that such a trial would have allowed the full details of the crime to be revealed.
"If there will not be a trial... a lot of this information that people want to hear about... may not come to light," said victim Richard Friedman.
'Money we need'
Investigators say they are now continuing efforts to recover $177bn from Madoff. He himself estimates that the fraud totalled $50bn, and investigations have only managed to recover $1bn so far.
1) Scheme leader convinces individuals to invest an amount that will deliver big returns
2) Leader takes deposit (eg $100) from original investors promising to double it within a month
3) Leader needs four more investors to pay promised returns ($400) to original depositors as leader has pocketed their $200
4) To pay out his returns the scheme leader now needs to find eight investors
5) If the scheme continues 16 investors will have to be found, and so on
"Because of the nature and length of the scheme, victims may recover only a small fraction of their losses," added Mr Dassin.
Some victims have also been paying taxes for a number of years on profits that have turned out to be fake.
Under current US rules, taxes can only be reimbursed for the past three years, but Madoff's fraud started in at least the early 1990s.
"We were paying taxes on money that didn't exist. We paid a fortune," said victim Lenore Schupak, 55.
"This is money we need to live on," added Ms Schupak, who said she had been forced to sell her home and move in with her sister.
Authorities have yet to make any comment on whether Madoff victims will be able to claim back taxes from more than three years ago.
Wall Street stalwart
A former chairman of the Nasdaq stock market, Madoff had been a Wall Street figure for more than 40 years.
Madoff ran a Ponzi scheme, whereby early investors were paid off with the money of new clients.
While he said it only started in the early 1990s, prosecutors say it began in the 1980s.
Madoff has pleaded guilty to 11 charges - four counts of fraud, three counts of money laundering, making false statements, perjury, making a false filing to the US financial watchdog, and theft from an employee benefit plan.
He could been sentenced to 150 years behind bars .