US News

FATAL BREAK-UP

The man suspected of fatally slashing his Ivy League girlfriend’s throat in their Chelsea apartment before leaping to his death from a Financial District high-rise committed the savage murder right after she broke up with him, sources said yesterday.

Margaux Powers, 26, had canceled plans to attend a family gathering Thursday – the night she was killed – so she could break the news to Jonathan Smith, 34, about the end of their troubled relationship and her desire that he move out, the sources said.

Powers, a Glen Cove, LI, native who worked for Estabrook Capital Management, was found dead Saturday night by her sister and a doorman in the bathtub of the fifth-floor apartment at 235 W. 22nd St., where she had recently moved in with Smith.

“Oh, my God, he finally did it, he finally did it!” wailed her sister Dana Powers after making the grisly discovery, according to a neighbor, Gracian DeVivo.

“It was awful, hearing her screaming,” said DeVivo, 43, who also said she heard Dana call Smith “a raging alcoholic.”

Dana Powers and the doorman, Constantine Ionescu, had entered the apartment the day before looking for Margaux, a former Connecticut prep-school lacrosse star, but hadn’t checked the bathroom.

“The family was worried,” Ionescu said. “They said he [Smith] had a bad temper.”

When Dana and Ionescu returned Saturday night and found the 2005 Cornell University grad’s corpse, cops began calling around for Smith.

On the bathroom floor was an unsigned, one-page, handwritten note in which Smith apologized to his victim and her mom.

Two hours later, at 10:08 p.m. Smith, who recently had been fired as a chef at the newly opened Café Society near Union Square, leaped from 25 Broad St.

“It sounded like a ‘boom!’ ” said Louis Bonilla, 22, who was a block away when he heard Smith’s body land in front of the sparsely occupied 24-story building, which is undergoing renovation.

It was not clear why Smith, whose father works in finance, chose to jump from that building, known as The Exchange.

Workers at the nearby Lamacha Pizzeria said he visited the eatery often.

Cops have determined that Smith used a butcher knife from the apartment to slash Powers’ throat, the sources said. Afterward, he cleaned the apartment and the knife, which he heated in the oven in an apparent attempt to get rid of blood traces on it, the sources said.

Powers’ father, Michael, said in a statement, “We are completely devastated by the loss of Margaux. She was an extremely loving and loyal daughter, sister, granddaughter and a joy to our family.”

A man answering the phone at the Palm Beach Gardens, Fla., home of Smith’s family would said only, “I have no interest in talking about Jonathan.”

But a Smith family friend said Jonathan – known as Jo-Jo – was “one of those kids struggling with addiction.” Ironically, the friend said, when he and Margaux were seen together recently “they looked like the perfect couple.”

Additional reporting by Matthew Nestel, Joe Mollica, Anne Wilner and Jamie Schram

larry.celona@nypost.com