Why legal prosecution of computer crimes require superior computer forensics

It’s really unfortunate when you read stories like this. Julie Amero, a substitute teacher in the Connecticut area, has been battling the state on a porn pop-up case that landed her four felony pornography convictions in early 2007.
A team of pro-bono computer forensic experts examined a ghost image of the hard drive and found numerous errors in the prosecution’s case which lead to overturning of the trial and it went to a new trial last June. Amero plead guilty to a misdemeanor of disorderly conduct, paid a fine and is moving on with her life.
Unfortunately for this particular situation, I think that Threat Level reported on the spot. The prosecution’s technical expertise was flawed in many cases and the testimonial didn’t jive with the evidence given by what the forensic evidence provided by the hard drive. Even giving up her state teaching credentials is asking too much of someone that didn’t actually click the pop-up links from malware judging by the analysis report of the ghost image given by the defense’s technical experts.
I assume that the prosecution wouldn’t let the charges drop even due to this overwhelming evidence due to the fact that four years down the line, they had already committed to many resources that it a dropped case would have looked bad. While I’m no legal expert, I believe that the misdemeanor was a justification of internal politics that happens in all stages of corporate and government alike.
A copy of the report by the forensics team can be found here.