The prosecutor didn't need a PR firm. He had a lurid story to tell, misinformation to divulge, diaries to secretly release, etc. The parents were left to combat a barrage of pre-trial publicity in a foreign country and often in a language they didn't speak.
So you enjoyed the movie? I think there were some errors, but the facts of the case came through. The Knox PR firm did a pretty good job of keeping most evidence under their hats, but that's all over now.