The presumption of innocence IS THE CORRECT ATTITUDE. Humans have an illogical tendency to jump to conclusions, presume guilt, and go on witch hunts. Presuming innocence until proven guilty by facts is the best way to stop that irrational behavior and protect the innocent. Someone who like child porn and intentionally seeks it out (and is therefore believed to be directly or indirectly a danger to children, the whole reasoning behind child porn being illegal in the first place) is not going to download one video, delete it, and never download it again. Everything about the circumstances points to his story being correct, Limewire is famous for misnamed files, and its not the first time I've heard of there being kiddie porn on it. He did not have a collection, nor did he have it even saved, it was clearly deleted. There is no evidence he distributed it, sought it, or wanted it. If there is more to this case the FBI needs to reveal it, of course they won't have to because they have used the fact the legal system is rigged in their favor in this kind of case to scare him into a plea bargain.
I know someone who is happily married, with 2 children. Their family has a very difficult time finding a place to live. The reason? When the Father was 18, he had consensual sex with his future wife, who was 16. Her family found out and pressed statutory rape charges. As a result, he is on the sex offender list, which is especially ironic because the "punishment" now hurts the supposed victim, and her children. The state has done far more harm to her then he ever did.
The police have no interest in justice. Every time you see a policemen, do not think he is there to protect you, or seek justice. His sole purpose is to be a crony to a politician, whether that politician is the DA, or the Mayor, or the governor, or the President. His job is to implicate as many people as possible in as many violations of the law as possible, to be used against them at his masters discretion. Every politician wants to look tough on crime, especially on pedophiles, and keep the population certain that HE is the one standing between their children and the groping hands of molesters. So the police are encouraged to round up as many people who can be labeled pedophiles as possible, and make sure the public is constantly reminded they are walking amongst them.
Just look at this article. The FBI tells people if you download child porn accidentally, call the authorities immediately. Presumably so they can offer you a plea "bargain" like this guy for turning yourself in, and only give you 3.5 years, plus 10 years parole, and a lifetime of discrimination on the sex offenders list. It is the exact opposite of what any competent lawyer would tell you to do, which is never admit to anything, never talk to the police, never allow them in your house, car, or computer without a warrant.