Though Mr. Gilbert’s courtroom tantrums may have given the jury the impression that he’s mentally unstable, not everyone saw him as a mentally disturbed man in the months leading up to his father’s murder.

Two ex-girlfriends and his uncle described him in testimony as “shy” and “awkward,” but said they did not see signs of severe mental illness, nor did they think he was a murderer in the making.

The witnesses said Mr. Gilbert seemed more concerned with maintaining an easy going lifestyle than following his father’s footsteps. His father, who attended Princeton and Harvard Business School, went into finance and founded Wainscott Capital Partners Fund.

His uncle, George Seymour Beckwith Gilbert, a merchant banker living in Connecticut, testified that he had spoken to his younger brother about Mr. Gilbert’s lack of ambition. He said he felt he had a right to speak up because he had paid for his nephew’s Princeton tuition.

“I said he ought to get a job,” he testified. “That’s the way we were brought up,” he added. “We always worked summers after we were 16. And we were expected to get a job when we got out of school.”

Yet the younger Mr. Gilbert seemed unconcerned with making his own way, his uncle said while trying to keep a steady tone of voice. He said his nephew did not reply to emails that included suggestions about job opportunities.

Instead Mr. Gilbert asked his uncle for a recommendation so he could join the Devon Yacht Club, an upscale social club in the Hamptons. He already frequented both the Maidstone Club in East Hampton and the River Club in Manhattan.