SAN FRANCISCO-The federal investigation of Barry Bonds approaches a key juncture Thursday, with the grand jury probing the baseball star for perjury and tax evasion set to expire and a possible indictment of Bonds looming.

Bonds’ personal trainer, Greg Anderson, also was awaiting a key ruling from a federal appeals court that could release him from prison, where he was sent earlier this month after refusing to testify against his childhood friend.

Anderson likely holds the key to whether perjury charges could stick against Bonds, who testified in 2003 that he thought substances given to him by the trainer were arthritis balm and flaxseed oil.

Authorities suspected Bonds was lying and that those items were “the clear” and “the cream” -two performance-enhancing drugs tied to the BALCO, the lab exposed as a steroids supplier to top athletes in baseball, track and other sports.

“Obviously, they think they need Greg to prove perjury,” Mark Geragos, Anderson’s lawyer, said Wednesday.

Allegations of steroid use long have plagued Bonds, who passed Babe Ruth in May to become second only to Hank Aaron on the career home run list. They intensified in late 2003, when he testified before the original Bay Area Laboratory Co-Operative grand jury, which took testimony from about two dozen athletes.

Anderson’s status is one of many legal uncertainties surrounding the San Francisco Giants slugger.

Without the trainer’s help, prosecutors still could indict Bonds on charges alleging he failed to pay taxes on money made through sales of autographs and other memorabilia. They also could seek to extend the grand jury’s term to put more pressure on Anderson to cooperate, or convene a new panel and put Anderson back in jail. There’s also the chance Bonds might be indicted on perjury charges without Anderson’s testimony.

Federal prosecutors declined to comment Wednesday.

THE ASSOCIATED PRESS