The way I understand it, there were allegations in 1998 that were investigated by the PSU police (I know there was a situation where a janitor walked in on Sandusky sucking off a young boy up against a wall - not sure if that was this one, though). No charges were filed, but Sandusky suddenly retired at 55 in 1999. Obviously we don't know, but that sure smells like he was fired, but allowed to resign and retain all on-campus privileges.
2002, a grad assistant caught Sandusky in the showers late at night with a 10 year old boy. Some reports say he observed Sandusky having anal sex with the boy, but not every report mentions that, so take it for what it's worth. He told Paterno, Paterno told the AD. Nobody at PSU contacted the police, nothing ever happened legally. PSU's response was to tell Sandusky he could no longer bring kids on campus. They didn't stop him from molesting, but they did stop him from doing it on their property. Another young man has alleged that Sandusky molested him in 2005, but PSU doesn't seem to be involved in that one, other than in helping Sandusky remain on the streets at that point.
I totally agree with you that we, of all people, should be careful of jumping to conclusions. But the eyewitness statements here, and the actions that followed them, are pretty hard to dismiss. At this point, Sandusky seems to be the only person saying that nothing happened, with a great deal of evidence that something did. My problem with JoePa is that 1) he is now claiming to be "shocked" by this, when he was given eyewitness evidence almost 10 years ago. That doesn't give him much credibility. And 2) that JoePa stayed silent after telling his supervisors. He's JoePa - if he pressured the higher ups to take action, they would have. If he had gone to the police and reported this, they would not have fired him. In his position, if there were any legal action or investigation happening, he would have known. He knew there wasn't. He knew there was a child molester running a children's charity in their community, and he did and said nothing for a decade. Maybe you can find the moral high ground in that, but I can't.