NEW YORK - Bernard Madoff claims he ran his multi-billion-dollar Ponzi scheme alone, but his close family will be sued this week in a widening probe, the government-appointed trustee told CBS television Sunday.

Trustee Irving Picard and his chief lawyer David Sheehan told CBS television's 60 Minutes program that Madoff relatives and many so-called victims profited massively.

For example, Madoff's immediate family used the fraudulent investment firm "like a personal piggy bank," Sheehan said, while major investors earned billions of dollars - possibly in full knowledge that this was a scam.

"We've found that there have been quite a few people who have gotten out more than they put in," Picard said.

The allegations are behind a legal onslaught stretching far beyond Madoff, who is serving the first months of a 150-year prison sentence.

Lawsuits are expected to be filed by the trustee this week against Madoff's sons Mark and Andrew, his brother Peter and niece Shana, CBS reported.

Picard is charged with finding where Madoff's billions vanished so that genuine victims - some left penniless after entrusting everything to the fraudster - can be compensated.

Just before his arrest and the collapse of his pyramid scheme in December last year, Madoff sent clients a statement claiming his fund was worth about US$64.8 billion (S$91.9 billion).

Picard and Sheehan, who rarely talk directly to the media, estimate the scheme in reality contained US$36 billion. They say half of this was disbursed before the collapse, while the other US$18 billion disappeared.

So far, Picard has snared just US$1.5 billion, including revenues from such easy targets as luxury residences in Manhattan, Long Island and Florida kept by Madoff and his wife Ruth.