This is indeed a two part question. How much did Jeremy know (as well as LE) in the beginning, and how much knowledge have they since gleaned? It is very difficult to say because nothing is really being released.
Time doesn't stand still in an investigation, and alot is going on behind the scenes. It doesn't help to say people are "gleeful" for the parents to be arrested, I believe everyone here just wants justice for Baby Lisa, and whoever is responsible, be it the parents, and intruder, et.al. be brought up for charges.
Hopefully, if we ever find out who is responsible, we will find out why. Finding out why this happened, may help us as a society, learn more, help more and save more children.