The former baseball great is accused of lying when he told Congress in 2008 that he had never used steroids or HGH .
McNamee is far and away the government 's key witness , the only person who will claim firsthand knowledge of Clemens taking performance - enhancing drugs .
The former baseball great is accused of lying when McNamee told Congress in 2008 that McNamee had never used steroids or HGH .
McNamee is far and away the government 's key witness , the only person who will claim firsthand knowledge of Clemens taking performance - enhancing drugs .