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Former baseball player Matt Williams testified Thursday that he refused an offer from private investigator Anthony Pellicano to wiretap the phone of his second wife.

"It's an illegal act," Williams testified.

Williams was the first prosecution witness called in the wiretapping trial of Pellicano and four co-defendants.

Prosecutors said Pellicano, 63, was the architect of a thriving criminal enterprise that raked in more than $2 million by spying on Hollywood's rich and famous then supplying the dirt to their rivals.

Clients "would pay a premium fee to discredit, and in some cases destroy, their adversaries," Assistant U.S. Attorney Kevin Lally said in his opening statement.

Among those allegedly targeted by the scheme were Sylvester Stallone and comedians Garry Shandling and Kevin Nealon.

Williams, whose 17-year baseball career was spent mostly with the San Francisco Giants and Arizona Diamondbacks, testified that he paid Pellicano $25,000 in December 2001 to investigate his first wife because he was concerned about the safety of their three children.

Within a month, Williams and Pellicano talked about the possible monitoring of his then-wife, Michelle Johnson, who was living in Los Angeles, apart from her husband.

Prosecutors played a recorded conversation between the two men in which Pellicano suggests he could "keep an eye" on Johnson by listening to her private conversations. Williams said he didn't know he was being recorded by Pellicano.

Williams, a five-time All-Star who retired in 2003, is among dozens of players named in December in the Mitchell Report as having used performance-enhancing drugs. He now works as a broadcaster for the Arizona Diamondbacks.

The recording is one of more than 70 audio recordings prosecutors intend to introduce as evidence against Pellicano, who is accused of wiretapping phones and bribing police and telephone workers to intercept conversations that could give his clients an advantage in legal disputes.

Lally called Pellicano a prolific snoop who also taped his own discussions with clients. He said a treasure trove of recordings seized during a 2000 FBI raid on Pellicano's office paint a "clear and crystal" picture of the detective's shady dealings.

In that sense, "he's the biggest government informant in this case," Lally said.

Pellicano, acting as his own attorney, spoke for only 10 minutes during his opening statement, contending he recorded and encrypted his own calls only as a way to create a referencing system.

Because he was acting as his own lawyer, Pellicano was told by the court to refer to himself in the third person when he addressed jurors.

"His presumption was that these conversations would be made available to no one but him," Pellicano told the panel.

He also said he prided himself on being a secretive person who treated the problems of his clients as his own.

Lally said Pellicano took extreme measures to cloak his alleged illegal activities, recruiting senior law enforcement officers and telephone company employees who didn't need much supervision, then talking to them in code.

In addition, he rigged a wiretapping software program known as Telesleuth so no one else could access the recordings, Lally said.

Omerta, an Italian word meaning code of silence, was used as a password.

Among those allegedly enlisted by Pellicano were retired Los Angeles police Sgt. Mark Arneson and former telephone company employee Rayford Earl Turner. Other co-defendants in the case are Kevin Kachikian and Abner Nicherie. All have pleaded not guilty.

Seven people have pleaded guilty to a variety of charges including perjury and conspiracy. Six of the seven, including film director John McTiernan and former Hollywood Records president Robert Pfeifer, are expected to be called as witnesses.

Attorneys for Arneson and Turner told jurors the evidence won't show that their clients were part of a criminal enterprise, and that they didn't even know each other before they were arrested two years ago.

Arneson may have crossed a line by providing a "shortcut" for Pellicano in searching government databases, but he wasn't a corrupt officer and was paid by the private detective for legitimate private security work, attorney Chad Hummel said.

Adam Braun, who represents Kachikian, said in his opening statement that Pellicano hired his client to develop the eavesdropping software.

Braun said Kachikian thought the software would be marketed to law enforcement agencies: "He didn't know it was going to be misused on wiretaps."

Pellicano could provide some fireworks when he cross-examines some of his former clients and employees. Federal prosecutors filed a list of 127 potential witnesses that included Stallone, Chris Rock and Shandling. It was not clear, however, how many people would actually testify.

Other prominent Hollywood players on the potential witness list include one-time Walt Disney Co. president and agent Michael Ovitz; Brad Grey, chairman and chief executive officer of Paramount Pictures; and Ron Meyer, president and chief executive officer of Universal Studios.

One of the first witnesses will be retired baseball player Matt Williams, who had a bitter divorce battle in 2002 with his second wife, actress Michelle Johnson.

Prosecutors said in a court filing they have an audio recording of Williams and Pellicano but didn't elaborate on its content.

The trial is expected to last about 10 weeks.