In short he was caught running a paedophile and prostitution ring for the mega rich and famous a few years back. At that time he was very controversially allowed to make a plea bargain together with massive pay outs to victims and got away with a very low sentence.
That let a lot of people off the hook, but left a scandal haunting them of course.
More recently there've been new allegations and it's been made clear that this time there are no deals. Consequently a lot of people in high places have been expecting him to implicate them in exchange for a deal.
It's a story which has been running for years in the States and I don't think anyone disputes his guilt plus he's been convicted once but gotten away without a serious sentence and that's a controversy in itself.