Federal prosecutors may be pursuing a perjury case against San Francisco Giants slugger Barry Bonds, stemming from his denials of steroid use during a federal grand jury appearance in 2003, multiple sources have told CNN.
For more than a month, a different federal grand jury has been hearing evidence about whether Bonds may have lied during his testimony on December 4, 2003, the sources told CNN.
The U.S. attorney's office in San Francisco would neither confirm nor deny that a grand jury has been hearing testimony about Bonds.
Bonds' lawyers were unaware that a grand jury had been convened, said Harry Stern, a spokesman for his legal team.
Bonds, who now ranks third in career home runs, has steadfastly maintained he never knowingly used steroids. He was one of several prominent athletes called to testify as part of an investigation into BALCO, a San Francisco Bay Area laboratory accused of distributing steroids and other performance-enhancing drugs.
At the time, Bonds and the other athletes were given immunity by federal prosecutors, provided they told the truth on the stand.
Bonds' attorney, Mike Raines, has previously accused prosecutors of trying to set Bonds up for a perjury charge by offering him immunity to get him in front of the grand jury, then later challenging his testimony.
BALCO's founder, Victor Conte, spent four months in jail after pleading guilty to distributing illegal steroids. Greg Anderson, a long-time friend of Bonds, was sentenced to three months in jail on the same charges.
Bonds' denials came under renewed scrutiny in March with the release of the book "Game of Shadows" by San Francisco Chronicle reporters Mark Fainaru-Wada and Lance Williams.
The book alleges Bonds used steroids and other performance enhancing drugs for at least five seasons, starting in 1998, and that Anderson -- his personal trainer -- helped him obtain the drugs.
Bonds has sued the authors to try to block them from making any money on the book, which his attorneys say was based on illegally obtained grand jury transcripts.
In the wake of the controversy over "Game of Shadows," Major League Baseball Commissioner Bud Selig appointed George Mitchell, a former U.S. Senate majority leader and federal judge, to investigate steroid use in baseball.