I don't recall off the top of my head how they blew that particular one.
They couldn't even make the liquor charge stick, and that seemed their strongest case - I think the conspiracy charge was over-reaching and made the whole thing shady. The prosecutor looked as though he had a personal vendetta, and was willing to put liars on the stand if it meant getting Jackson.
The prosecuter had to try. I think it's pretty obvious what a danger to children this creep is.