At the Den of Volokhs, David Bernstein says:

"Michael Jackson: The last boy who accused Jackson of molestation received a $12 million settlement even though his claim was uncorroborated, and, in the view of many who followed the case closely, of dubious veracity. Given the obvious financial incentive of a family to fabricate a claim, it's going to be awfully tough to get a conviction in the current case unless the police have turned up additional evidence."

Actually, I was thinking that knowing past history and the ability of Jackson to defend himself, they must either a) be pretty damned sure they have a solid case -- i.e., stronger evidence than was present in past accusations --- or b) be complete idiots.

We shouldn't rule out b), however...