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Nearly five years ago, Thomas Gilbert Jr. showed up unannounced at his parents’ Midtown Manhattan apartment and asked to speak alone with his father about business.

Minutes later, his father, a hedge fund manager, lay dead with a gunshot to his head and Mr. Gilbert was running from the police .

As details emerged, the murder stunned New York’s high society, in which the Gilberts were well known. The police said Mr. Gilbert, a Princeton graduate who was never able to obtain consistent employment, had killed his 70-year-old father because his weekly $1,000 allowance was cut. He became a symbol of ungrateful greed, a child of privilege who turned to murder when he feared he was losing his lavish lifestyle.

A jury found Mr. Gilbert, 35, guilty of second-degree murder and gun charges in late June, rejecting an insanity defense. And on Friday, a state judge in Manhattan, Melissa Jackson, sentenced him to life in prison, with a possibility of parole after 30 years, the maximum penalty allowed under the law.