Federal prosecutors trying Barry Bonds for perjury have so far presented a strong case with testimony from several witnesses that the record-setting retired baseball player did in fact use steroids, say legal experts.

But that case – and whether the jury buys it or not – is beside the point, they add. The question the government needs to prove, they say, is whether or not Mr. Bonds lied about it in 2003 testimony to a grand jury investigating alleged steroid use.

Bonds, Major League Baseball’s record-holder for home runs in a career (762) and a season (73), is being tried at the federal courthouse in San Francisco, accused of lying to a federal grand jury for testifying in 2003 that he never knowingly used performance-enhancing drugs.

“They’ve put on a well-organized case that has done just what they said it would at the beginning, which is to show through multiple witnesses that Bond’s physique changed, he had mood swings, showed aggression,” says Caleb Mason, a professor of law at Southwestern Law School in Los Angeles.

He says the judge may still instruct the jury to throw out certain details they have heard – specifically some, but not all, of the testimony from a former girlfriend who might be motivated to smear Bonds. And, Professor Mason says, the defense has yet to put on its case, which is likely to concede Bonds’ use of steroids but deny that Bonds knew about it.

“The defense has several story lines they can go after, from the possibility that he was a guinea pig for his trainer testing relatively new substances, to the motivation of his mistress to get revenge after he cut her off,” says Mason.

Testimony from ex-girlfriend

On Monday, 41-year-old Kimberly Bell testified that she became Bonds’ girlfriend when she was 24 and he was in the process of divorcing his first wife. She said he told her in 1999 or 2000 that he was using steroids and that he blamed the drugs for an elbow injury.

Ms. Bell said that from 1999 to 2001, Bonds “was just increasingly aggressive, irritable, agitated, very impatient."

The defense’s cross examination of Bell took more than five hours and became so heated that the US District Judge Susan Illston told defense lawyer Cristina Arguedas to “ratchet it down.”

The trial’s proceedings got an infusion of additional baseball star-power Tuesday afternoon with the testimony of the Giambi brothers, Jason and Jeremy, both of whom have admitted to steroid use.

Jason Giambi, currently the Colorado Rockies first baseman and the 2000 American League Most Valuable Player, testified that he received performance-enhancing drugs and instructions on their use from Greg Anderson, Bonds's former trainer, who is jailed for refusing to testify.

Also testifying was former San Francisco Giants outfielder Marvin Benard, who said Mr. Anderson injected him with a steroid around 1999.

Both Giambis said Anderson mailed them products of the Bay Area Laboratory Cooperative (BALCO) that were undetectable steroids, and told them how to use them.

'I understood what it was'

All three players said Anderson told them what the substances were.

“I understood what it was; a steroid,” Jeremy Giambi said of his conversations with Anderson.

On the stand Jeremy Giambi was asked if Anderson ever told him what he was taking was flaxseed oil, a substance that Bonds has said he thought he was applying. Giambi replied, “no.”

Earlier Tuesday, prosecutors called two witnesses to discuss the urine samples Bonds provided during the 2003 season, alleging those samples tested positive for the designer steroid THG.

The two witnesses, Barry Sample, chief science officer of Quest Diagnostics, the company that analyzed Bonds’s urine, and Dale Kennedy, who collected the sample, were essential to establish that Bonds’s samples were handled properly and can be used as evidence.

The aim of the baseball players’ testimony was clear: to show that Bonds would had to have known that the substances his trainer had given him were steroids.

But the reason perjury is hard to prove is that one must be able to establish beyond a reasonable doubt what the defendant was thinking at the time of the alleged perjury, analysts say. That means one must clearly establish an internal mind set based on external behavior.

There is also the problem of jury instruction about the legal standard needed for conviction. “Jurors sometimes get confused by that standard [“beyond a reasonable doubt”], says Eldon Ham, adjunct professor of sports law at Chicago-Kent College of Law.

“It does not mean beyond any doubt, or beyond ridiculous doubt, but rather beyond ‘reasonable’ doubt. What is reasonable?”