After a case has been completed and a person is convicted there are still many legal steps that can be taken to determine what happens next. There is still the possibility of an appeal assuming that a case can be built. In an appeal, new evidence may be presented or old evidence may be cited as being inaccurate or flawed due to something specific to the case.
The only way to determine that a case could be overturned on appeal is to look at the facts of the case. Hiring someone to do case study research on your case to see what might be able to be pointed out on appeal is a good idea. This can help a lawyer find reasons why an appeal should be made and have ideas about what issues to raise during the appeal.