"Mark Madoff took his own life today. This is a terrible and unnecessary tragedy," his lawyer, Martin Flumenbaum, said in a written statement.
His body was found hanging from a dog leash that had been fashioned into a noose and strung over a pipe in the ceiling of his living room, according to a law enforcement official. The official was not authorized to speak publicly about the case and spoke to The Associated Press on the condition of anonymity.
"Mark was an innocent victim of his father's monstrous crime who succumbed to two years of unrelenting pressure from false accusations and innuendo. We are all deeply saddened by this shocking turn of events," Flumenbaum said.
Mark Madoff and his brother, Andrew, were under investigation but hadn't faced any criminal charges in the massive Ponzi scheme that led to their father's jailing.
Bernard Madoff swindled a long list of investors out of billions of dollars and is serving a 150-year prison term in North Carolina. He was arrested on Dec. 11, 2008, after confessing his crimes to his family.
Madoff's sons, according to the family's attorneys, were the ones who turned him in.
The scandal put a harsh light on members of the family. The financier's brother, Peter, played a prominent role in the family's company. Mark and Andrew Madoff both worked on a trading desk at the firm, on a side of the business that wasn't directly involved in the Ponzi scheme.
In February, Mark Madoff's wife, Stephanie, petitioned a court to change her last name and the last names of their two children, saying her family had gotten threats and was humiliated by the scandal.
Law enforcement officials told The Associated Press that Mark Madoff's wife, who is in Florida, became concerned about her husband after getting a communication from him either Friday night or early Saturday morning suggesting that someone should check on their two-year-old child.
She asked her father to check on the home. When he arrived, he found the body, as well as the two-year-old sleeping safely in his bedroom.
A dog in the apartment was also unharmed.
A call to Bernard Madoff's attorney was not immediately returned Saturday. Calls to the FBI and U.S. Attorney's office were also not immediately returned. Previously, spokespeople for the brothers had repeatedly denied that they had any knowledge of their father's crimes.
A year ago, the court-appointed trustee trying to unravel Madoff's financial affairs sued several relatives, including Peter, Mark and Andrew, accusing them of failing to detect the fraud while living lavish lifestyles financed with the family's ill-gotten fortune.
The lawsuit accused Mark Madoff of using $66 million he received improperly to buy luxury homes in New York City, Nantucket and Connecticut.
Police investigators were at Madoff's apartment Saturday morning, along with officials from the medical examiner's office, which will determine the cause of death.