The killing gripped New York City when it was first reported.

A Princeton graduate with movie star looks was accused of entering his hedge fund father's tony NYC apartment and fatally shooting him. His mother-- who he asked to get him a Coca-Cola from a store-- found her husband's body in his bedroom.

The trial was never about who pulled the trigger; it was about whether or not Thomas Gilbert Jr., was aware of his actions at the time of the shooting.

On Friday, a state judge in Manhattan ruled against the killer and sentenced him to the maximum sentence allowed: 30 years to life. Prosecutors said Gilbert knew what he was doing and "threw the ultimate tantrum" after having his allowance slashed.

Gilbert addressed the court for about 10 minutes and referred to himself as "the defendant," The New York Times reported.

He told the court, “The defendant expresses remorse.”

Justice Melissa Jackson was not convinced that he is insane.

"You knew exactly what you were doing," she said, according to the Times. "You were not insane at the time you killed your father. You were not insane then. You are not insane now."

Thomas Gilbert Sr. was fatally shot on Jan. 4, 2015. The younger Gilbert showed up unannounced, angry that he lost his weekly allowance of $1,000. According to prosecutors, he spent the money on travel, memberships to elite sporting clubs and other personal expenses, but was not able to hold down a steady job.

His parents, who also covered his basic daily expenses, had been encouraging him to become more self-sufficient and incrementally reduced his monthly allowance.

Shelley Gilbert, his mother, insisted after the sentencing that her son was mentally ill and could not comprehend his actions. The New York Times reported that she pleaded with the judge to order her son to be admitted to a psychiatric facility.

“I know this is what my husband would have wanted for him,” she said.

The jury rejected the 35-year-old defendant’s insanity defense during the trial, deciding that he murdered the hedge fund manager with a shot to the head at close range from a semi-automatic pistol, a .40-caliber Glock purchased months earlier from a seller in Ohio. Before fleeing the apartment, Gilbert put the gun in his father’s hand to try to stage his death as a suicide, according to trial testimony.

“Thomas Gilbert, Sr. was a beloved member of his family and business community when his own son murdered him in a cold-blooded killing,” District Attorney Cyrus Vance said Friday in a statement. “But now, thanks to my office’s prosecutors, the defendant has finally been held accountable and he will serve a life sentence for this unconscionable crime.”

The elder Gilbert was the founder and manager of the New York-based Wainscott Capital Partners Fund.

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His son also was convicted on charges of criminal possession of a weapon.

The Associated Press contributed to this report