The former chairman of Sotheby's was portrayed on Monday first as a greedy boss who cheated customers out of millions of dollars through a price-fixing scheme and then as a man betrayed by a power-hungry subordinate.

After three weeks of testimony, the jury heard closing arguments in the federal conspiracy trial of A. Alfred Taubman, 76, of Bloomfield Hills, Mich. He and former Christie's Chairman Anthony Tennant are accused of stealing as much as $400 million in commissions from sellers from 1993 to 1999.

Jury deliberations were set to begin Tuesday. If convicted, Taubman would face up to three years in prison.

The prosecution's case centered on testimony by Diana "DeDe" Brooks, the former chief executive for Sotheby's, who pleaded guilty in October 2000 to price-fixing charges. She agreed to testify against Taubman in hopes of avoiding a three-year prison sentence.

In his closing arguments, defense attorney Robert Fiske attacked Brooks' credibility — referring to her plea deal — and said her story was full of holes.

"DeDe Brooks is a walking reasonable doubt," Fiske said.

He also accused Brooks of being the one who set up the agreement to fix prices on sellers' commissions during a February 1995 meeting in the back seat of her car with her counterpart at Christie's, Christopher Davidge.

"We agree with the prosecution that a crime was committed," Fiske told the jury. "The question for you is whether Mr. Taubman had anything to do with that agreement."

The auction houses together control more than 90 percent of the world's art auctions.

Brooks, 51, testified that the plot was conceived during a secret 1993 meeting in London at which Taubman and Tennant agreed they "were killing each other on the bottom line, and that it was time to do something about it."

During testimony, Brooks and Davidge said their bosses ordered them to end a costly rivalry by eliminating discounts and charging identical, non-negotiable commissions. Brooks said Taubman also warned her to keep quiet about it.

The secret deal denied sellers the right to negotiate a lower commission from one auction house by threatening to take business to the other. Since some auction items are worth millions of dollars, negotiating even part of a percentage less could translate into considerable savings for the seller.

In closing arguments for the prosecution, John Greene, of the Justice Department's antitrust division, told the jury that Taubman had the motive, the capacity and the opportunity to carry out the price-fixing conspiracy.

Sotheby's profits started shrinking in the late 1980s, from $410 million in 1989 to $202 million in 1992, and Taubman's stock in the company had plummeted as well, Greene said. As chairman of the company, Taubman had the power to put such a conspiracy in place, Greene said.

As for opportunity, Greene cited Brooks' testimony about the meetings with Tennant that she said Taubman told her about.

"The fix was in," Greene said.

During testimony, the defense presented witnesses who portrayed Brooks as a power-hungry CEO who felt that she, not Taubman, ran Sotheby's. Meanwhile, Taubman ignored the auction house's pricing policies and was so bored by finance that he would nod off at meetings, perking up only when the subject turned to lunch, defense witnesses said.

In his closing arguments, Greene sought to counter that image, telling the jury that a man of Taubman's wealth who sat on the boards of several companies could not be a "know-nothing."

Greene said the jury should reject the idea of a "dumb and hungry Taubman."

Tennant, 71, of Andover, England, has said he will not come to the United States to face charges, and the antitrust case is not covered by extradition treaties.

Sotheby's pleaded guilty to conspiracy and was sentenced to pay $45 million. Christie's was granted amnesty by the government for its cooperation.