Lawyers for Brooke Astor’s only child, Anthony Marshall, are asking a judge to consider the possibility that motherly love — not theft — explains how he ended up with so many of the late philanthropist’s prized possessions.

In legal papers filed yesterday, Mr. Marshall’s lawyers asked Judge A. Kirke Bartley to dismiss an indictment alleging that Mr. Marshall, 84, looted his mother’s assets and accounts in her final years. Astor died last year at the age of 105, prior to the prosecution of her son by the office of the Manhattan district attorney, Robert Morgenthau.

Mr. Marshall’s lawyers say that nobody is in a position to prove that Astor didn’t instruct her son to make the very expenditures he is now accused of undertaking without her permission. Those expenditures include $600,000 in upkeep on a Maine estate that she had transferred to her son.

“Mrs. Astor and her son were frequently alone together, and therefore they alone witnessed these conversations between them,” the legal brief states.

More generally, defense lawyers questioned why prosecutors would be suspicious about the fact that Mr. Marshall had ended up with much of Astor’s money.

“Mrs. Astor was Mr. Marshall’s mother,” the defense lawyers wrote. “It is common for a mother to give her only child property, and there can be no presumption, particularly given the evidence of Mrs. Astor’s generosity to Mr. Marshall, that merely because Mr. Marshall obtained property from Mrs. Astor that it was a theft.”