Disgraced financier Bernard Madoff is facing the prospect of spending the rest of his life behind bars after admitting a massive investment fraud. In a court in New York, the 70-year-old pleaded guilty to all 11 charges relating to an estimated $50 billion "Ponzi" scheme, where investors are paid from the proceeds of other investors rather than profits. Prosecutors have indicated that they will push for the maximum sentence of 150 years in prison. Madoff, dressed in a grey suit, appeared calm in court as he pleaded guilty to each of the 11 charges in turn. He told the court: "I am grateful for this opportunity to publicly speak about my crimes, for which I am so deeply sorry and ashamed." He added that he knew his actions were "wrong" and "criminal" when he set up the Ponzi investment scheme. "I believed it would end shortly and I would be able to extricate myself and my clients from the scheme," he said. But as time went on it proved "difficult" and then "impossible" to end. He said: "As the years went by, I realised my risk, and this day would inevitably come." But the guilty plea suggests he is still refusing to co-operate with authorities over the whereabouts of missing billions or who else may have been involved in the scheme. The 70-year-old has been under house arrest in his luxury penthouse on Manhattan in New York since his arrest on December 11.