So is the forestry service also part of the prosecution? The state revenue service? What about the judges? They are part of the State...does that mean they are also part of the prosecution?
No it isn't.
The prosecution is the DA's office conducting the prosecution, no one else. It is their mandate to enforce the laws that are on the statute books within the area of their jurisdiction. The police investigate an alleged offence, and turn the results of the investigation over to the DA, who then decides if a prosecution is warranted or not. The police are supposed to be neutral and are not involved in the prosecution at all, but they do report to the DA. That is why they have to hand over everything in their investigation file. Agencies outside of the responsible police force may provide assistance, but have no obligations. They can assist the responsible police force, or they can choose not to. They do not report to either the DA or the local police force. In the case of the TBI they report to the state AG, and the state AG is not the prosecutor in the prosecution. The AG and DA may not even like each other and have fundamental disagreements about what and how things should be done. Information gathered by the TBI that is provided to the local LE cannot be concealed at that point, that is where the constitutional issues would start, not the actual gathering part. So, for example, if the TBI does a DNA analysis on request from local LE and hands it over to the sheriff, that cannot be concealed. But if they do a DNA analysis on their own initiative and keep it to themselves, it is not part of the official investigation or the body of evidence. And they can do this because they are at arms length to the whole process and do not report to the principals.
That is the problem in this case. Effectively most of the investigation is being done and run by the TBI, but they don't report to the DA. That means that not everything about the investigation is necessarily reaching the DA, what he receives is a second hand version, essentially only the information that they have chosen to provide to the local sheriff. IMO the TBI clearly has an agenda here and an opinion about how the case should progress, an opinion not necessarily shared by the local DA. The DA has to seek out any information that other agencies or organizations have, they are not obliged to proactively hand over anything they might have to him. And if he doesn't know what information they have, and they don't like the way he is doing things, he is going to have a hard time getting it. There is inter-department politics involved in these sorts of things, they are not all one big happy family working towards a common goal. And because they report to different people, who may have different agendas, cooperation is not a given. This is how things work in real life in government bureaucracy, like it or not.
That is what happens everywhere else in the country. Perhaps Tennessee is different.