The National Football Post has an excellent article on the delay in the case against Tom Cable that was written by a former district attorney. In this article he outlines that the longer it takes for the charges to be filed, the more likely it is that there is not corroborating statements from the other coaches who were present at the time. That along with Hanson's changing statements make the delay appear to indicate nothing is going to happen.
In domestic violence situations, it’s true that prosecutors often proceed even if the victim refuses to cooperate. But what enables prosecutors to do so are usually the victim’s initial statements -- sometimes a 911 call or remarks made to a police officer or caregiver -- or the observations of an officer on the scene. Those first-impression statements, often considered the most credible in any case since witnesses are coached as time goes on, can then be introduced as evidence. But Hanson’s first statements are that nothing happened. So Lieberstein’s office seems to be struggling with his credibility. I’ve never heard of a battered-assistant-coach syndrome to explain away conflicting statements.
Basically, what this means is that Hanson sabotaged the potential case against Tom Cable right off the bat by protecting the team with his initial statements.
It's also true that every witness testifies under penalty of perjury; the vast majority of criminal convictions for perjury do not involve testimonial perjury but intentionally attesting to false facts in documents. It's rare that someone is tried, let alone convicted, for lying on the witness stand, especially when "I do not recall" is a virtually perjury-proof statement. Prosecutors don't like to try people for perjury and want to avoid witness-stand surprises even more. So it's unlikely that Lieberstein will want to bring a case against Cable unless all the other people in the room at the time of the alleged assault corroborate Hanson's version of events. No prosecutor would just want to put witnesses on the stand and let the chips fall where they may. Prosecutors are expected to get convictions and are careful about the kind of cases they elect to try. As long as there's a difference of opinion about what witnesses observed, it may be enough to deadlock this matter, especially given Hanson's conflicting statements.
Despite the indelible image left by generations of Perry Mason reruns where he gets a witness to breakdown on the stand confessing to everything, that is not the reality of modern jurisprudence. The prosecutor wants to know what is going to happen before he starts his line of questions. It would be difficult for the Napa County prosecutor to build a case using hostile witnesses.
Lieberstein may also be trying to deal with issues involving the Raiders’ relationship to his county and the revenue they bring by holding training camp there. I think it’s remote that Lieberstein might be looking into a possible cover-up involving Cable and perhaps stretching higher up in the Raiders organization. It would explain the delay, but we aren’t talking about the crime of the century here.
Rooting out a vast Silver and Black conspiracy may make a great novel, but it is doubtful that the Napa County district attorney is looking to do that with the limited resources available in the case of a broken jaw.