He was testifying before a federal grand jury investigating the Bay Area Laboratory Co-Operative, or BALCO, and had just been shown what prosecutors say was a positive steroid test conducted on a player named Barry B.

"I've never seen these papers," Bonds repeated, according to yesterday's indictment charging Bonds with perjury and obstruction of justice.

Those test results may now be the vital linchpin to proving he lied under oath.

Bonds' lawyers are expected to fiercely attack their reliability, much the way O.J. Simpson's legal team undermined the football star's murder case by questioning the handling of his blood samples.

Bonds' attorney, Michael Rains, declined to comment. But BALCO founder Victor Conte offered some insight today into how the slugger's legal team might cast doubt on the evidence.

It was November 2000, and Bonds was preparing for the season in which he would shatter Mark McGwire's single-season home run record.

According to Conte, himself a convicted steroids dealer, Bonds would visit the lab on Saturdays and after normal business hours with an entourage that included his trainer, Greg Anderson, and his personal physician, Dr. Arthur Ting.

Anderson had convinced Bonds to use BALCO to develop a dietary and supplement regimen, which Conte designed based on the results of the blood and urine samples.

Conte said Bonds was put through the same tests as other elite athlete clients, including tests to detect the use of 30 different steroids.

Conte hired Quest Diagnostics to do a "quick and dirty" analysis of the samples, to save money. The lab charged Conte $80 per test, rather than its usual $120, after Conte agreed to cut out much of the paperwork and elaborate protocol that typically accompany drug tests.

For instance, Conte said a licensed lab technician never watched Bonds urinate in the bottle. Nor were the samples ever formally sealed, dated and signed by an independent collector. There was also no formal process for who handled the samples at Quest, Conte said.

The indictment does not explain where prosecutors obtained the results, but Conte said they were seized when federal agents raided his lab in September 2003.

"If that's the smoking gun," Conte said, "it doesn't have any bullets."

The U.S. Attorney's office in San Francisco declined to comment.

Criminal defense attorneys not affiliated with the case say the reliability of blood and urine tests are always open to second-guessing even when the forensic handling is done flawlessly.

"There is always an opportunity to attack that kind of forensic evidence through its chain of custody," said attorney William Sullivan, who recently won an acquittal for former federal prosecutor Richard Convertino on an obstruction charge alleging he withheld evidence in a terrorism trial in Detroit.

"You look at how the evidence was preserved, who handled it," Sullivan said. "You can even attack the analysis itself."

Similar chain-of-custody problems exploited by Simpson's lawyers helped derail the prosecution's murder case against him.

Los Angeles County prosecutors argued that DNA testing on blood, hair and fibers collected at the murder scene proved Simpson's blood and the blood of the two victims were present.

But Simpson's defense team was able to cast doubt on whether the evidence tested was the same as that collected at the scene by showing that each piece of DNA evidence was handled by at least three people before it was tested.

The problems with the Simpson evidence prompted law enforcement agencies to adopt more stringent protocols. Few of those protocols were followed in collecting and analyzing Bonds' blood and urine, Conte said.

"I don't think you can prove those were Barry's samples," he said.

Another vulnerable spot in the government's case is Anderson's steadfast refusal to testify against Bonds.

Because federal prosecutors were so adamant that the trainer should go to prison for refusing to testify, the trainer's lawyers — and most other observers — believed Anderson's testimony was necessary to indict Bonds.

But Anderson was released from prison Thursday and, according to his lawyers, he never cooperated with the investigation. He could land back in prison, however, if prosecutors decide to call him as a witness during the trial and he refuses to testify.

Criminal defense attorneys said other parts of the government's case against Bonds are ripe for attack — none bigger than the testimony of his former mistress, Kimberly Bell.

In 2005, Bell told a grand jury investigating Bonds for perjury that the slugger told her he used steroids. But Bell is open to withering cross-examination, lawyers said.

Rains said she was miffed that Bonds didn't pay her the nearly $200,000 she demanded when their 10-year relationship ended in 2003. Bell said she was asking Bonds to keep a promise to buy her house in Arizona, but Rains said the demand amounted to extortion.

The indictment cited 19 instances in which Bonds lied during his grand jury testimony, including several denials that he took performance enhancing drugs.

Little other evidence is presented in the indictment, but that doesn't mean prosecutors don't have something else up their sleeve, legal experts said.