Jurors in the murder trial of pampered Princeton graduate Thomas Gilbert Jr. said their guilty verdict eventually turned on a can of soft drink.

“The can of coke: it was really our ‘aha’ moment,” juror number 11, Steven David Torres, said.

The juror was referring to the moment when Gilbert showed up unannounced at his parents’ Turtle Bay apartment in New York on January 4, 2015 — and sent his mum Shelley Gilbert out for a Coke and a sandwich.

Shelley Gilbert testified that her son knew full well that she never kept that beverage in the house.

The panel of 12 jurors was initially split on Gilbert’s case and wrangled for two contentious days on whether to find him not guilty by reason of mental defect.

“There was a lot of emotion, one side just yelling, ‘He’s guilty! He’s guilty!’ and the other side was like, ’He’s not, he’s sick,’” Torres said.

Then another juror reminded the panel that Gilbert had asked his mum for the can of Coke to get her out of the house so he could fatally shoot his hedge fund millionaire father Thomas Gilbert Sr.

The court heard the 34-year-old showed up to his parent’s apartment, pressed a .40 caliber Glock against his dad’s temple and pulled the trigger.

The 70-year-old collapsed on the floor of his bedroom as his son fled.

He was enraged that his parents’ had slashed his allowance and the soft drink request showed how clear-headed and calculating he was when he committed the crime, several jurors said.

“It was a light bulb moment for me,” juror number eight, Julie Thiry-Couvillion, said.

Gilbert had failed to find steady employment after graduating from Princeton with a degree in economics, instead living off his parents’ largesse.

They bankrolled his lifestyle of leisure, paying for international surfing trips, country club memberships, a Chelsea rental apartment and a Jeep.

When his father threatened to take all that away, Gilbert retaliated.

Defence lawyer Arnold Levine told jurors that Gilbert had suffered from schizophrenia for more than a decade and was unable to maintain a job. It was psychosis and paranoia, not greed that spurred him to kill his father, Levine argued.

“Tommy didn’t understand or appreciate the consequences of his actions,” the lawyer said, urging the panel to find Gilbert not guilty by reason of mental defect.

His mother paid the tab for his private lawyer and has repeatedly said her son belongs in a hospital, not prison. Shelley Gilbert was the prosecution’s reluctant star witness, testifying against her son after she was subpoenaed.

Unlike many of the jurors, Linda Corcelles-Alvarez said she never wavered on her belief in Gilbert’s guilt.

“It was all about money. He just shot him in cold blood,” Ms Corcelles-Alvarez, juror number 10, said.

Torres added that most of the panel believed he suffered from severe mental illness but “not at that moment he committed the crime.”

In a 911 call played at trial, the operator asked the woman who shot her husband and she replied, “My son, who is nuts. But I had no idea he was this nuts.”

Photos of Gilbert taken just before the murder reveal a strapping blond surfer, with model good looks.

A string of ex-girlfriends who testified at his trial said his behaviour was strange but he was so handsome they overlooked it.

Since his incarceration, he has unravelled mentally and physically, often babbling incoherently in court with his oversized shirts and slacks hanging off his frail frame.

Gilbert is due back in Manhattan Supreme Court on August 9 for sentencing.

This article originally appeared on The New York Post and has been republished here with permission.