With his fortune under assault and federal investigators focusing more attention on him, Mark Madoff, the 46-year-old son of the architect of Wall Street's greatest scam, took his own life in his Soho apartment yesterday, New York City police said.

Madoff, who had been a key official in Bernard Madoff's investment firm, was found hanging by a black dog leash from a pipe in the living room of his apartment, two years to the day after his father was arrested by the FBI in a Ponzi scheme that destroyed the lives of thousand of investors, wiped out charities and decimated estates.

Madoff was discovered by his wife's stepfather about 7:30 a.m. Saturday, police said. Madoff's wife, Stephanie, in Florida with their 4-year-old daughter, became concerned about the well-being of the couple's 2-year-old son after an exchange of e-mails with her husband, a police official said. She alerted her stepfather, who discovered Madoff in the couple's apartment at 158 Mercer St.

The son was asleep in a nearby bedroom and unharmed, along with the family dog, police said.

Madoff had sent at least two e-mails to his wife and one to his lawyer in the early morning, a police official said. In the e-mails to his wife, he asked her to take care of their son and said that he loved her, the official said.

"This is a terrible and unnecessary tragedy," Martin Flumenbaum, the attorney representing Mark Madoff and his brother, Andrew, said in a statement. "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."

In recent weeks, federal investigators had charged a number of Bernard Madoff associates in indictments. The latest under indictment was key operative Annette Bongiorno, who was charged last month with fabricating documents and securities fraud in connection with the Ponzi scheme that investigators believe lost investors $20 billion.

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Agents investigating the scheme recently had focused more attention on Mark Madoff, one investigator said.

"He was next up to the tee," said the investigator, who didn't want to be named because of the pending probe, referring to the shift of attention to Mark Madoff.

Mark Madoff wasn't viewed as a major insider with vast knowledge of his father's fraud but he is believed to have had some awareness of the fraudulent nature of the operation, the investigator said.

Irving Picard, the bankruptcy trustee in the Bernard Madoff case, said Mark Madoff, Ruth Madoff and Andrew Madoff knew or should have known about the fraud when they received tens of millions of dollars from the investment company.

Picard sued the Madoff family members, including Mark, last year and also this past week in an effort to get back any profit that they may have received from the scheme.

"This is a tragic development, and my sympathy goes out to Mark Madoff's family," Picard said in a statement yesterday.

One person who had recent contact with Madoff told The Associated Press that he was despondent over coverage of his father's case and his struggle to rebuild his life.

The intense scrutiny approaching the anniversary "became too much for him," the person said.

Ira Sorkin, the attorney for Bernard Madoff, said he had been trying to reach out to the Federal Bureau of Prisons to learn if his client had been told of the death of his son. Madoff is serving a 150-year prison term in North Carolina.

"This is a great tragedy on many levels," said Sorkin.

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Calls to relatives of Ruth Madoff in Florida, with whom she is believed to be living at times, were not returned.

Mark and Andrew Madoff had turned their father over to the FBI on Dec. 10, 2008, after Bernard Madoff confessed to them that his investment business was a scam and had caused massive losses to investors. Bernard Madoff was arrested a day later.

Investors of the defunct Madoff firm were saddened by Madoff's death.

Jeff Wilpon, chief operating officer of the New York Mets, who went to Roslyn High School with Madoff in the 1980s, said, "It is shocking, it is sad, it is tragic."

Wilpon, who said in December 2008 that Mark Madoff had been a friend of his for 30 years, has been sued along with other members of his family by Picard in one of hundreds of lawsuits the trustee has filed to get back profits from Madoff investors.

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Richard Friedman, 61, an accountant from Jericho who lost money investing with Bernard Madoff, said no one was taking any joy in the son's suicide. "We see this as a family tragedy," said Friedman. "Nobody envisioned this happening, nor did anybody want Mark Madoff to kill himself."

Stephanie Madoff, Mark's wife, petitioned a Manhattan court in February to change her and her children's last names to Morgan to avoid harassment and threats.

Mark Madoff graduated from the University of Michigan. He was a licensed broker with his father's firm since 1987. He has two other children from a previous marriage, ages 18 and 16. Madoff and his first wife, Suzanne, divorced in 2000.

Reported by Yamiche Alcindor, Sophia Chang, Emily C. Dooley, Anthony M. DeStefano, Keith Herbert, Bart Jones, David Lennon, Emily Ngo