How would the criminal justice sysytem be altered if state attorneys general were given authority to supervise locally elected DAs?
Most district attorneys are elected by the people of the county. This makes the prosecutor accountable to the people who elected him. If he were to be supervised by the state attorney general, then the election would have to be removed from the process. He cannot answer to the state attorney general and to the people. That will also mean a new method for selecting him will have to be applied. If he is to be appointed by the governor or the attorney general, then in doing his job, he may consider the political ramifications of his actions as prosecutor. Having the prosecutor elected and accountable only to the people of the county means that he does his job in accordance with the wishes of the people. The people are likely to elect someone who is more in keeping with the ideology of the area - whereas a governor would appoint someone more in keeping with the governor's ideology.
In my state, District Attorneys are elected by the people of the Judicial Circuit, but are under the supervision of the State Attorney General. The AG does not have power to "fire" the DA, but he can supervise, and take over the prosecution of a case if/when he feels it advisable. Also, if the DA is involved in any questionable activity, the Governor has the right to suspend him pending resolution of the matter, and can remove him for good cause shown. By this method, the local populace has some control over the administration of justice in the local circuit; however at the same time, there is some uniformity of justice throughout the state.