Even if Giants slugger Barry Bonds is charged with lying to a grand jury, it will be hard to convict him, former federal prosecutors and other lawyers said. "It is a lot tougher to make a perjury case than most people think because it takes more than just proving that the person made a statement that was untrue," said Adam Hoffinger, a criminal defense lawyer in Washington D.C. "The government has to prove that he knowingly and willfully lied about a material fact ? it can't be a mistake, there has to be intent." A federal grand jury is investigating whether Bonds committed perjury when he testified in 2003 that he never used steroids, a person with knowledge of the probe told The Associated Press on Thursday night. The person spoke on condition of anonymity because of the secrecy of the investigation.