Marshall is Astor's child from her first marriage, and they reportedly were not always close. "They had a complicated relationship," Gordon said. "She loved her son, but I don't think she always liked him."
Prosecutors are expected to argue that Marshall and Morrissey knew of Astor's declining mental state and exploited it to trick her into giving him millions of dollars.
Among other allegations, Marshall is accused of telling his mother that she was running out of money in order to convince her to sell one of her beloved Childe Hassam paintings for a reported $10 million, taking $2 million as commission.
Though Marshall would have inherited a substantial amount of money in any case, he is also accused of arranging changes to her will to give him control over her fortune, most of which was previously supposed to go to charity.
Lawyers for Marshall and Morrissey are expected to argue that Astor was mentally capable of approving the changes, and that Astor loved her son and wanted to reward him financially.
"We are confident that Mr. Marshall will be vindicated," one of his lawyers, Fred Hafetz, said. A lawyer for Morrissey did not return a call for comment.