irving picard gave us a tour of bernie madoff's 19th-floor offices, an impressive landscape of emptiness. >> his desk was here. >> safer: picard has the thankless task of finding the money, the billions that madoff scammed. (watch ticking) arlan galbraith who called himself "the pigeon king" convinced hundreds of american and canadian farmers there was good money to be made raising the birds for food. >> and everybody we talked to said this guy was--he was on the up and up. nobody had a bad word to say about him. (watch ticking) >> stahl: welcome to "60 minutes" on cnbc. i'm leslie stahl. in march 2009, bernard madoff pleaded guilty to perpetrating what's believed to be the largest financial fraud in history. he received the maximum sentence for his crime, 150 years in prison. but while madoff is behind bars, there's still much we don't know about the scam which involved, by some accounts, a fraud of more than $50 billion. investigators are still trying to figure out who was involved and where the money went. this edition features some of the people most intimately familiar with madoff's

wife ruth and his son andrew, lived with vilification, shame, and pursuit from bankruptcy trustee irving picardis lead counsel david sheehan. they were demanding that the madoffs cough up virtually every penny they have, claiming they, quote, "knew or should have known" about bernie's crimes. >> would you agree with mr. sheehan, the lawyer for the trustee, when sheehan says you should be ashamed, that you should give every penny back? >> well, obviously, i disagree with many of the assertions in the lawsuit that the trustee has filed against me. and i'm hopeful that, in time, we'll be able to reach a settlement, and i'll be able to put this behind me. >> picard says the sons' trading operation received millions from bernie's ponzi scheme. he is suing andrew madoff alone for $60 million, virtually every penny he earned, borrowed, or was given to him by his father over a ten-year period. let me ask a really intrusive question. how much are you worth as we speak? >> well, i was fortunate over the years, running the business that mark and i ran. it generated many millions of dollars in profits and

>> reporter: irving picard is the trustee appointed to recover funds from madoff and has secured aboution of the estimated 17.5 billion dollars invested with madoff. two big highlights, 7.2 billion- dollar deal with a madoff associated who died and a $162 million settlement of the owner of the new york mets. the trustee hopes to recover an additional $3 billion over the next year and a half. that leaves investors with about a $5 billion total loss. >> wow. the scandal was a wake-up call for investors. what can we do to protect ourselves against this? >> reporter: i think you always need to start by asking questions. you want to determine whether your broker or advisor will be handling the advice. the trading or the custodianship where your assets are held. the lesson of madoff is interesting. you should avoid advisors who control all three aspects of the investment process. in most firms, at least one of those pieces is handled separately. that allows for a third party to conduct checks and balance. the next thing is of course be cynical about stellar returns never type of market. that