San Francisco (CNN) -- Barry Bonds' childhood friend Steve Hoskins, who worked for a decade as his assistant, testified Wednesday in Bonds' perjury trial that he tried to convince him to stop using anabolic steroids in 2000 and 2003.
Hoskins, a key prosecution witness, was grilled by Bonds' defense lawyer, who suggested his cooperation with the government was motivated by his bitterness toward being fired by Bonds and protection from prosecution for allegedly stealing money from Bonds.
Major League Baseball's home run king is charged with four counts of lying to a federal grand jury about his use of steroids and one count of obstruction of justice. Each count could carry a 10-year prison sentence.
Prosecutors must convince a jury of eight women and four men that Bonds knew his trainer Greg Anderson was giving him illegal steroids and that he lied about it in December 2003 in testimony to the grand jury that was investigating what became known as the BALCO scandal.
Former IRS agent Jeff Novitzky, who uncovered the steroid scandal among world-class athletes with his relentless investigation of BALCO, a California blood-testing lab, testified before Hoskin.
Novitzky, who now works for the FDA, testified that BALCO provided performance-enhancing drugs to a long list of professional baseball and football players, track and field athletes, swimmers and pro cyclists.
Barry Bonds' grand jury testimony was "inconsistent with the facts," Novitzky testified Tuesday.
Prosecutors played for jurors Wednesday an audio recording that Hoskins secretly made in the San Francisco Giants locker room of a conversation with Anderson about the hazards of steroid usage.
Bonds' defense lawyer Allen Ruby suggested that Hoskins only made the recording after Bonds fired him in March 2003. Hoskins acknowledged that he leaked the details of the recording to investigative reporter Lance Williams, who included it in his book about the scandal, "Game of Shadows."
His first conversation with Bonds about performance-enhancing drugs was in 1999, when Bonds asked him to "find out what this steroid does and what the side effects are and was it good or bad," Hoskins testified.
Hoskins said that he followed Bonds' instructions to talk to his personal physician, Dr. Arthur Ting, about it.
While he never witnessed Bonds being injected with anabolic steroids, Hoskins said he witnessed Bonds and Anderson emerge from a bedroom with a syringe during spring training in 2000.
Bonds complained to him in 2000 that steroid injections "were making his butt sore," Hoskins
The subject of steroids came up again in 2002 during a conversation among Bonds, Anderson and Hoskins near the batting cages at the ball park, Hoskins said. Bonds was upset because Anderson refused to give him an injection, he said.
"Barry just said if Greg wouldn't give him a shot, he would give it to himself," Hoskins testified. "He was just upset that Greg wouldn't do what he wanted him to do."
Hoskins testified that he noticed Bonds was growing "a lot more muscular" and that he required bigger shoes and gloves. "It just seemed to be getting out of hand," Hoskins said.
He spoke to Bonds' father, retired Major League player Bobby Bonds, about his concerns in 2000 and again in 2003, Hoskins testified.
Jurors heard an audio recording of a conversation that Hoskins said he secretly recorded with Anderson in 2003 to prove to Bonds' father that his son was using steroids.
"I was hoping Bobby would be the one to get them to stop doing it," Hoskins said. Bobby Bonds died the same year of cancer.
In the muffled recording, made in the Giants locker room, Hoskins asked Anderson about the hazards of steroid injections not properly done.
"What happens is they put too much in one area and what it does, it will actually ball up and puddle," Anderson said.
"Is that why Barry didn't just shoot it into his butt all the time?" Hoskins asked.
"No, I never just go there, I move it all over the place," Anderson said.
While Anderson never refers to injecting Bonds, he does not object to Hoskins' reference to injections.
Under cross-examination, Hoskins acknowledged that he secretly recorded the conversation after a meeting with Bonds in which the ballplayer severed their business relationship.
Hoskins testified that his break with Bonds happened because Bonds wanted him to spend more time with him at the ballpark, but he had to help his wife with a new daughter.
"Barry told me at that time I had to choose between him and my wife," Hoskins testified.
One of Hoskins' jobs as Bonds' assistant was to give cash, sometimes in $5,000 installments, to two of the married baseball player's girlfriends, he testified. It was also his job to help Bonds juggle his time with those girlfriends and his wife during spring training in Arizona, he said.
Testimony in the San Francisco trial started Tuesday with Anderson refusing to testify against him, prompting the judge to send Anderson to a prison until he changes his mind or the trial ends.
Anderson has been sent to prison twice before in 2006 for refusing to testify against Bonds before a grand jury investigating his alleged perjury. He also served a short prison sentence after pleading guilty in 2005 for his involvement in the BALCO scandal.
"He doesn't trust the prosecution," his lawyer, Mark Geragos, said. "He will never cooperate with these guys."
The trial, which is expected to last three or four weeks, is taking place less than two miles from the ballpark where Bonds, 46, broke Hank Aaron's home run record in August 2007. Then a star on the San Francisco Giants team, Bonds was indicted three months later.
Assistant U.S. Attorney Matthew Parrella told jurors that a urine sample given by Bonds in the summer of 2003, just months before his grand jury testimony, tested positive for anabolic steroids.
Defense lawyer Allen Ruby, in his opening statement, told jurors that Bonds acknowledged to the grand jury that he used the substances known as "the clear and the cream," but at the time of his testimony even investigators didn't know what was in it.
Bonds told the grand jury he thought Anderson was giving him flaxseed oil, Ruby said.
"Barry answered every question, he told the truth, he did his best and, most significantly, he provided the grand jury with useful information which supported the indictment that they later returned against the BALCO defendants," Ruby said.
Novitzky testified Tuesday that he fished through the trash at BALCO every week for a year starting in the summer of 2002, searching for evidence of money laundering and illegal drug distribution.
A magazine clipping he found in the garbage bin led him to Bonds as a witness, he said. It included a photo of Bonds with BALCO chief Victor Conte and Anderson, indicating that Bonds "was using their services," Novitzky testified.
Bonds' ex-girlfriend, Kimberly Bell, will testify later that Bonds told her he was taking steroids prior to the 2000 Major League Baseball season, according to the prosecution.
The prosecution said Bell would "testify to personal observations regarding changes in the defendant's body during the period of time beginning in the year 1999, including bloating, acne on the shoulders and back, hair loss, sexual dysfunction, and testicular shrinkage," all physical indications of steroids use.
Ruby, in his opening statement, attacked Bell and Hoskins as having "very pervasive, very strong" bitterness toward Bonds.
Bell, he said, was still angry about the bitter break-up of their decade-long relationship.
These witnesses "cooperated with the media as anonymous sources on many of the poisonous things about Barry," he said. "They have tried to create a caricature of Barry Bonds, a terrible guy, always bad, mean and so on."
Several former teammates implicated in the BALCO scandal are also on the witness list to testify for the prosecution.
Bonds holds the major league record for home runs with 762 in his 21-year career. He also set the record for most home runs in a single season in 2001 when he hit 73 balls out of the park.
Bonds did not officially retire after he was indicted, but he never played another game.