Faced with a possible 150 year jail term, Bernard Madoff is thought to be considering whether he should plead guilty to other uncharged offences. This could be a way of improving his privileges during his sentence.
Criminals pleading guilty to crimes often ask for other crimes to be taken into consideration because they know that law enforcement agencies and the District Attorney's office are keen to clear up unsolved crime without extensive detection and court costs. It means the criminal cannot be charged with those offences later, and in some cases it makes the difference in the category of prison facility, or the prisoner's cell furnishings.
Bernard Madoff has not yet said which crimes he is likely to admit to, but speculation by the press includes running the Mafia, responsibility for the Enron fraud, hiding weapons of mass destruction in Iraq, the Iran Contra scandal and the assassination of Kennedy.
If he were to plead guilty to these crimes his 150 year sentence would be carried out in his own home, except for times when he wanted to go out.