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New York • A prosecutor urged a jury on Wednesday to find a professional Las Vegas gambler linked to golfer Phil Mickelson guilty of earning tens of millions of dollars illegally in the stock market.

Assistant U.S. Attorney Brooke Cucinella told jurors in closing arguments that evidence they'd seen over the last three weeks proves that William "Billy" Walters pocketed more than $40 million illegally. She said trading and phone records back up the testimony of a former Dean Foods Co. board chairman who said he repeatedly gave secrets to Walters.

"We're here because Billy Walters cheated, not once, but over and over and over again," the prosecutor said of criminal activity alleged to have gone on for at least half a decade.

She cited the proximity of phone communications between Walters and former Dean Foods board chairman Thomas Davis and stock trades made by Walters as proof that the gambler used secrets from Davis to cheat in the market.

She noted Walters bought 1.5 million shares of Dean Foods stock minutes after Davis left him a phone message after Davis learned from a board meeting conference call that the Dallas-based company, one of the nation's largest processors of milk for retailers, was spinning off part of its business and was about to surprise the market with robust earnings.

Cucinella said Davis owed Walters nearly $1 million at the time from a loan Walters had given him.

Walters, 70, has pleaded not guilty. Davis, 68, has pleaded guilty to insider trading charges and was cooperating in the hopes of leniency at sentencing.

The prosecutor said Walters urged Mickelson to buy Dean Foods stock and the golfer then invested $2 million, scoring a profit in 2012 of nearly $1 million, which he turned over to Walters to cover gambling debts.

"Mickelson had never purchased Dean Foods stock before, not once," she said.

Cucinella said prosecutors do not know if Walters described his source of information about Dean Foods before Mickelson placed trades.

Mickelson was not charged criminally. But the Securities and Exchange Commission accused Mickelson in a civil lawsuit of making nearly $1 million in the stock trade. Mickelson agreed to repay it.

Before the trial, Mickelson was listed as a possible witness, but he did not testify.

A defense lawyer was scheduled to deliver a closing argument Thursday. In openings, attorney Barry Berke said Davis was lying about Walters to keep himself out of prison.

He praised his client, saying the Kentucky-born sports gambler had built a sprawling business of auto dealerships, car rental agencies and golf courses worth hundreds of millions of dollars and routinely made multimillion-dollar bets in the stock market.