Oct. 20, 2011  -- After being convicted in June 2009 of orchestrating the largest Ponzi scheme in American history, disgraced financier Bernie Madoff was sentenced to 150 years in a North Carolina prison.

But his daughter-in-law, Stephanie Madoff Mack, the wife of Madoff's oldest son Mark, felt he hadn't suffered enough. Mack wrote him a letter laying out the life he was missing, with details about the young grandchildren -- Mack's daughter Audrey and son Nicholas -- he would never see again.

The letter focused on "things that he would love to be part of, and now would never be part (of)," Mack said. "So I thought that that would really sting him."

But Mack said her plan backfired. Madoff's response, she said, sickened her. He described his life at Butner Prison -- which is considered a "crown jewel" of the federal prison system and is known for its college campus-like feel -- as one filled with "loads of friends" who respected him.

READ Bernie Madoff's letters from prison.

He wrote, "As you can imagine, I am quite the celebrity, and am treated like a Mafia don. They call me either Uncle Bernie or Mr. Madoff. I can't walk anywhere without someone shouting their greetings and encouragement, to keep my spirit up. It's really quite sweet, how concerned everyone is about my well being, including the staff...It's much safer here than walking the streets of New York."

Read Madoff's full letter here.

Mack said she was "smokin' pissed" and didn't show her letter to her husband Mark, who was already tortured by his father's unimaginable duplicity.

On Dec. 11, Mark Madoff committed suicide. His dead body was found hanging from a ceiling beam. (Read an excerpt of a letter Bernie Madoff wrote reacting to his son's death here.)

"My husband was in terrible, terrible pain," Mack said. "He was so deeply hurt by it all, that he just, he, he just couldn't move past it."

Mack has written a book on her life as a Madoff, "The End of Normal: A Wife's Anguish, A Widow's New Life," published by Blue Rider Press.

Read more about Mark and Stephanie Madoff here and watch the full story on "20/20" Friday at 10 p.m. ET.