Mr. Giesea and his wife on several occasions met with Mark Madoff and his wife, Stephanie.
"This is a tragic development, and my sympathy goes out to Mark Madoff's family, " he said.
In the years since high school, Jeff Wilpon and Mark Madoff had remained close friends.
It's currently for sale, according to a person familiar with Mark Madoff's finances.
Before his suicide last year, Mark Madoff had been writing his own memoir.
FORBES: Mark Madoff's Unpublished Memoir: 'My Father Has Stolen My Life'
In 2000, Mark Madoff was listed as head of trading for Madoff in stocks listed on the New York Stock Exchange.
Law-enforcement officials said Saturday Mark Madoff's father-in-law went to his apartment at the request of Ms. Morgan, who was in Florida.
Mr. Giesea said Mark Madoff had been using office space in Manhattan in recent months and pitching the idea to various potential partners.
Mark Madoff appears to have hung himself in his upscale Manhattan apartment with a black dog leash and was discovered Saturday morning by his father-in-law.
Mark Madoff's attorney, Martin Flumenbaum, on Saturday called his client's death.
More recently, the two talked about what Mark Madoff would do next professionally, after a seemingly successful career was abruptly stopped by his father's confession and arrest.
In the 1990s and 2000s, Mark Madoff headed trading desks for the firm, overseeing dozens of young men and women who dealt with traders at large banks and fund companies.
One filed on December 8 named Mark Madoff -- as well as his brother Andrew Madoff and uncle Peter Madoff -- as one of several defendants in a civil lawsuit.
Known as sociable and confident, Mark Madoff often went out with his trading colleagues and hit the circuit of conferences where traders met to talk about how stocks were bought and sold.
The Journal also reported this morning that Mark Madoff had unsuccessfully tried at one point to get a job in trading and had most recently been working to develop new applications for iPads.
Mark Madoff hanged himself last month.
FORBES: Mark Madoff's Will Provides Important Lesson: Keep Your Estate Plan Up-To-Date
"I view Mark as a friend, and I find today's news totally shocking, out of character and horrible, " said John Giesea, chief executive of the Security Traders Association, where Mark Madoff once served as a governor and president of the trade group's New York affiliate.
FORBES: Mark Madoff Found Dead, A Suicide; Latest Tragedy in Ponzi Scheme
Following a critical article about the Madoff firm in 2001 by Barron's, which raised questions about whether the secretive investment operation was legitimately generating returns, Mark Madoff, with Andrew watching nearby, addressed dozens of Madoff traders in the firm's offices, strongly arguing that the article was incorrect, and that Madoff's investment operation was legitimate, according to people who were there.
Mark and Andrew Madoff agreed with Mr. Picard not to transfer or sell certain assets.
This week, Mr. Picard sued children of Andrew and Mark, alleging that Ruth and Bernard Madoff transferred funds to them.
Also last week, Mr. Picard sued children of Andrew and Mark, alleging that Ruth and Bernard Madoff transferred funds to them.
WSJ: Trustee Will Move Ahead With Suits Filed Against Mark Madoff
Mark and Andrew were employees of Bernard L. Madoff Investment Securities LLC, though they worked in the trading section, allegedly separate from the fraudulent investment management and advisory divisions.
Press release: Incarcerated Ponzi schemer Bernie Madoff has decided not to attend the funeral of his son Mark, who committed suicide this weekend.
FORBES: Bernie Madoff Still Shameless - No, He Can't Attend Son's Funeral
应用推荐