(JTA) — Convicted fraudulent financier Bernie Madoff wrote in a letter that the pain he caused investors was “nothing” compared to the pain he has suffered from his sons’ deaths.

Madoff, who defrauded investors of billions of dollars in one of the largest Ponzi schemes in history, wrote in an email to NBC News Friday that his sons were unaware of his crimes and that they never forgave him.

“As difficult as it is for me to live with the pain I have inflicted on so many, there is nothing to compare with the degree of pain I endure with the loss of my son’s [sic.] Mark and Andy,” he wrote. “I live with the knowledge that they never forgave me for betraying their love and trust. As much as I tried to reach out to them in an attempt to explain the circumstances that caused my betrayal they could not find it possible to forgive me.”

Mark Madoff committed suicide in December 2010, on the second anniversary of his father’s arrest. Andrew Madoff died last year from cancer.

Several large Jewish institutions and charities fell victim to the Madoff scheme. Madoff was convicted of fraud in 2009 and is currently serving a 150-year prison sentence.

In the letter, Madoff claims his sons were uninvolved in the scheme.

“What is still my most important goal is to do everything in my power to protect their legacy, although neither of my son’s [sic.] were ever charged with anything,” he wrote.