An ivy-league educated Manhattan man charged with killing his wealthy father for reducing his $1,000 a week allowance appeared in court on Tuesday for the first day of testimony.

Thomas Gilbert Jr., 34, is facing murder, gun possession, and other charges in connection with the January 2015 killing of his father Thomas Gilbert Sr., a renowned Wall Street hedge fund manager.

A jury listened to an 11-minute recording of a 911 call made by his mother after the alleged killing. When asked who had shot her husband, Shelley Gilbert, who testified on Tuesday, replied: “My son, who is nuts. But I had no idea he was this nuts. He shot him in the head.”

Gilbert’s lawyers argued that their client’s mental state made him unfit for trial, citing a decade-long history of mental illness, including diagnoses of schizophrenia and bipolar disorder, The New York Times reported.

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Prosecutors, in turn, portrayed Gilbert as a “self-absorbed and vengeful son” who was angry that his father had slashed his allowance.

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“When he murdered his father, the defendant was fully aware of what he was doing, and he certainly knew it was wrong,” assistant district attorney Craig Ortner told jurors.