Bernard Madoff's last surviving son was under investigation for possible involvement in his father's multibillion-dollar Ponzi scheme until the day he died from cancer earlier this month.

Andrew Madoff had long maintained that he and his brother, Mark, who hanged himself in 2010, knew nothing of the massive fraud.

But two federal law enforcement officials said investigators never believed the brothers were unaware of the fraud and both were under investigation until their deaths. They spoke to The Associated Press on condition of anonymity because they were not authorized to discuss the case.

Andrew Madoff left behind a $16 million estate. A court-appointed trustee is taking aim at that the sons' money, filing a lawsuit this summer accusing them of using money from their father's scheme as their "personal cookie jar."