On its 12th day of deliberations following a 19-week trial, the jury convicted Marshall of 14 of the 16 counts against him, including one count of first-degree grand larceny, the most serious charge, The New York Times repoerted. Marshall, who is to be sentenced Dec. 8, could serve 1-25 years in prison.
His co-defendant, Francis X.Morrissey Jr., who did estate planning for Astor, was convicted of forgery charges. Marshall was found not guilty on another grand larceny charge and of falsifying business records. He was accused of stealing much of his mother's $180 million fortune.
Astor died in 2007 at 105.
The trial featured testimony from such luminaries as Henry Kissinger and Barbara Walters. It was delayed a few times because of Marshall's ill health. The 85-year-old is a World War II veteran who fought at Iwo Jima.
Prosecutors called many witnesses to testify to the progress of Astor's Alzheimer's disease to illustrate she could not have changed her will or given extra funds to her son. The defense contended she had moments of lucidity.
Beautician charged with giving client fatal silicone butt injection
Handler slams Piers Morgan: 'You're a terrible interviewer'