Can the detective working on the case ignore the case itself , and case in general ? It have been 8 month with no results. All of the conversation is over the phone and email. Is there anyone over the detective who can make him work faster.
You can ask to speak to the investigator's supervisor, but the case may be slow for reasons beyond his control. Staffing, case load, priorities, and even availability of witnesses or sources of information can effect follow-up.
It could be that the case is not as solid as you think it is. It could be that the DA or a supervisor wants something more. Who knows?
But, you are certainly free to speak to the investigator's supervisor to see if someone can explain things to you.
As was pointed out, this is not television. Investigations in the real world can take a long time and are subject to all manner of variables outside the control of the investigator. I have a fraud case that I have been working for almost 6 months now, and it is because other events keep getting in the way, two people I need info from are reluctant to meet with me, and a source of documents I need is not returning my calls. Until I can get something from one or more of these investigative leads, my case is pretty much dead in the water.
However, nothing prevents you from suing the guy. If you feel you have a case and you can prove your side of the case, then take him to civil court. At least that way you can get something going that is based upon YOUR timetable.