as law is, that's why so many lawyers

i am a baseball fan, one news puzzled me a lot. the famous or infamous star barry bonds took steroids or PEDs, fed authority pressured his dearest friend and trainer anderson many times, trying to obtain his testimony agaisnt bonds, but anderson every time refused, for this he was jailed sereval times and hsi family was also harassed by fed.

i know this was not double jeopardy, becuase he was surely offered totla immunity for his testimony. but if he wanted to keep his faith to his friend (which i admire alot, and many people shared my snetiment), how come the government had the power to prosecute a guy agian and again basically on the same offense (obstruction of jsutice on bonds' case)? to a law ignorant like me i think it's abuse of power by government