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Barry Bonds' penchant for turning longtime friends into bitter enemies might come back to hurt him in at least two significant ways at trial.

First, there's Steve Hoskins. He was once Bonds' closest friend and served as best man at the slugger's first wedding.

Then, there's Kimberly Bell, the home run king's girlfriend of 10 years, who dated him even after his first wedding. In fact, Hoskins' sister introduced Bell to Bonds after a San Francisco Giants game in 1994.

Each had a nasty falling out with the notoriously prickly slugger, and each is now expected to be a key witness for the prosecution if Bonds goes to trial for perjury and obstruction of justice. He was indicted last week for allegedly lying when he told a federal grand jury he never knowingly used performance enhancing drugs, and is likely to face prison time if convicted.

Hoskins and Bell each claim to have firsthand knowledge of Bonds' steroid use, making them extremely valuable witnesses. Yet both also are vulnerable to attack by Bonds' lawyers because of their severed relationships with the former Giants star and their own personal problems.

"If they were standing alone, their credibility would present a big problem for the prosecution," said Peter Keane, dean of the Golden Gate University law school in San Francisco. "But the problem for Bonds is the collective amount of all this stuff the prosecution appears to have: the change in his body, the lab results. All of these things taken together make for a significant prosecution case against Bonds."

Hoskins and Bonds were childhood friends, both growing up in San Carlos, a southern San Francisco suburb.

Their fathers were friends: Bonds' dad played for several major league teams during a 14-year career, and Hoskins' dad was a star lineman for the San Francisco 49ers.

They rekindled their friendship in 1993, when Bonds signed with the Giants as a free agent after spending the early part of his career in Pittsburgh.

Bonds made Hoskins his business manager and they launched a company called Kent Collectibles to sell Bonds' memorabilia.

Things fell apart in 2003 after Bonds accused Hoskins of forging his signature on at least two contracts and selling memorabilia without Bonds' permission.

Hoskins' attorney has said Hoskins told federal investigators that Bonds was a heavy steroid user. When the lawyer, Michael Cardoza, went public last year with Hoskins' tale he declined to discuss in detail how Hoskins knew about Bonds' alleged steroids use.

Cardoza said Hoskins followed through on a threat to tell federal prosecutors about Bonds' alleged drug use after the slugger complained to the FBI that Hoskins was stealing from him. Bonds did complain to the FBI, but the feds soon dropped their investigation of Hoskins and turned their sights on Bonds and his alleged steroid use.

"Stevie is going to get on the stand and tell the truth," Cardoza said in a brief interview Tuesday. "Barry ignited this whole thing with Stevie."

Bonds' attorney, Michael Rains, didn't return a call for comment. But he has previously accused Hoskins of turning into a government informant and vowed to portray him in court as a vengeful former business partner seeking retribution because Bonds accused him of stealing.

Cardoza denied Hoskins turned into a government snitch.

"Stevie was investigated and he was cleared. He was cleared because he in fact did nothing wrong," said Cardoza, who declined to discuss whether Hoskins ever testified before the grand jury investigating Bonds. "My guy is not a government informant. He never made any deal with the government."

Bell did testify before the grand jury, telling the panel in 2005 that Bonds confided in her that he used steroids.

According to Bell, the admission came after Bonds said he was jealous of the attention Mark McGwire garnered when he broke the single season home run mark in 1998.

"He was very envious of Mark McGwire," she said in a July interview. "He never said that was the reason, but I know it was."

She also testified that during spring training, Bonds' personal trainer Greg Anderson would often drop by Bonds' condo in the mornings with a satchel and the two would disappear behind a locked door in a bedroom.

Bell didn't return calls for comment this week.

She is expected to undergo withering cross examination if she is called to the stand. Rains has said he has "three banker boxes" full of incriminating evidence against Bell, including allegations that she demanded money from the slugger to keep quiet.

"Her motives and biases are fair game," said attorney Brian Getz, who is not involved in Bonds' case but did represent sprinter Michelle Collins in an earlier phase of the government's steroids investigation — as well as two other athletes he declined to name.

"She is at the intersection of passion and wealth and that makes her particularly vulnerable," Getz said.

Besides their alleged knowledge of Bonds' steroid use, Hoskins and Bell also were widely expected to provide the cornerstone of the government's tax evasion case against the career home run leader.

Hoskins has said he handed over to Bell $80,000 Bonds earned at an autograph signing session and the grand jury was investigating whether he reported the income on his tax returns.

Laura Enos, a lawyer who handles Bonds' business matters, didn't return a telephone call. But she has said it was Hoskins who gave Bell the cash to curry favor with Bonds, and to thank the slugger for helping him become rich by putting him in charge of a lucrative memorabilia business.

Enos said Hoskins also bought Bonds a $350,000 Bentley Rolls Royce, on which Bonds paid $150,000 in gift taxes.

When the indictment against Bonds was unsealed last week, there was no mention of tax charges, but several criminal defense attorneys speculated that the government could be holding those uncharged allegations as bargaining chips during plea negotiations.