Sorry, but this is a simpleton's perspective. It's black and white.
I am married to an attorney, an asst DA in fact. She's been doing this about 12 years (7 in prosecution), and works in the Superior courts here (rape, murder, agg assault, major drug cases, etc). There is no black and white in the criminal courts....it's not like Dateline or 20/20. It's what can be proved. Obviously, since the DA agreed to a deal relatively quickly they may have seen some weakness in case (could be any number of things).