true. I do remember them mentioning that while you have the main story case, there are other side cases that you can choose to work at your discretion, some of them having an effect, I think, on the main case as well as your character--maybe how you are perceived by the NPCs?
If this is all true, then having the cases (witnesses testimonies) be identical from one playthrough to the next (I honestly don't see how they couldn't be), could still change how the main case, or how other cases play out as you progress. Say you choose not to follow up on one witness for one case and focus on another, and that witness ends up dead or something, effecting your progress elsewhere.