Anthony Marshall now faces a mandatory jail sentence of at least one year and perhaps as many as 25 years after jurors delivered their verdict to end a five-month trial that revealed the New York society doyenne's sad decline. She was 105 and had Alzheimer's disease when she died in 2007.
The jury convicted Marshall of two serious counts, first-degree grand larceny and scheming to defraud, but acquitted him on some others. Jurors also convicted estate lawyer Francis X. Morrissey Jr., 66, of scheming to defraud Astor.
The trial had gone on longer than expected and the jury took 11 full days of deliberations before returning the verdict.
Marshall, wearing a dark suit, looked at the jurors as they were polled. His co-defendant, Morrissey, looked down but didn't betray any emotion. They will remain free on bail until their Dec. 8 sentencing.
"I'm stunned by the verdict," said Marshall's attorney, Frederick Hafetz. "We are greatly disappointed in it, and we will definitely appeal."
The trial peeked into high society from Park Avenue to Palm Beach as prosecutors told a Dickensian tale of upper-crust money-grubbing, with a demented grande dame at its center.
Marshall was accused of a range of tactics from scheming to inherit millions of dollars to simply stealing artwork off her walls. Morrissey was accused of helping manipulate Astor into changing her will to leave Marshall millions of dollars that had been destined for charity.
The case put Astor's famous friends, including Barbara Walters and Henry Kissinger, on the witness stand and her dark final years on display. Jurors heard how a beau monde benefactor renowned for her elegance and wit became a disoriented invalid fearful of her own shadow.
Prosecutors portrayed Marshall a former U.S. ambassador and Tony Award-winning Broadway producer as a greedy heir who couldn't wait for his mother to die, buying himself a $920,000 yacht with her money but refusing to get a $2,000 safety gate to keep her from falling.
Defense lawyers said Astor was lucid when she bequeathed the money to her only child and that he had legal power to give himself gifts while she was alive. She was keenly focused on her will, and she loved her son, they said.
Astor's last will, created Jan. 30, 2002, left millions of dollars to her favorite charities. Amendments in 2003 and 2004 gave Marshall most of her estate.
The trial delved into Astor's shadowy mental state, health problems, finances and family relations. Jurors got crash courses in topics ranging from estate planning to handwriting analysis, amid questions about whether the socialite's signature was forged on some will amendments.
Prosecutors called some 72 witnesses, from the socialite's prominent friends to an official at the company that made paper used in an amendment to her will.
Many of them testified about Astor's mental confusion in the last years of her life.
Walters described using a photo album to help Astor recall guests at her 100th birthday bash during a visit only months later. Kissinger testified that Astor didn't recognize former U.N. Secretary-General Kofi Annan at a party she threw for him in 2002.
Former Brown University President Vartan Gregorian recalled the normally decorous society dame making an awkward toast to Britain's Camilla Parker Bowles in 1999.
But defense lawyer Hafetz pointed to episodes he said showed Astor was cogent at times, such as a four-page, impeccably spelled letter she wrote to her close friend Annette de la Renta in November 2002.
Astor's third husband, Vincent Astor, was the son of multimillionaire John Jacob Astor IV. She took charge of her husband's philanthropic work after his death in 1959. Her efforts won her a Presidential Medal of Freedom, the nation's highest civilian honor, in 1998.
Marshall is her son from a previous marriage to stockbroker Charles "Buddie" Marshall, who died in 1952.
The criminal case against Marshall and Morrissey came after one of Astor's grandsons asked a court to remove Marshall from handling her affairs.
Philip Marshall accused his father of abusing Astor by letting her live in squalor while he looted her fortune.
A civil case concerning her will has been on hold while prosecutors pursued the criminal charges.