Interesting points here. My question is this: if you charge someone with kidnapping and they are acquitted, can the acquittal on this charge be used in the suspect's defense if he is later charged with other crimes related to his actions?
Along these lines, I seem to remember reading somewhere that prosecutors don't like to seek search warrants unless they're pretty sure they're going to find what they are looking for. Because if they don't, then the fact that they looked for evidence but didn't find any will have a worse impact at trial than if they never looked in the first place.
Probably won't do the defendant any good because if you are aquitted by a jury for kidnapping you certainly don't want the jury on the subesequent sexual assault trial to know that you had been accused of kidnapping. The defendant will want to get as far away from the kidnapping accusation as possible.
The only advantage that the defendant would gain is that the prosecutor cannot introduce any evidence that the victim was taken by force or against her will. The only issue would be whether she consented to the sexual assault and/or whether she had the legal capacity to consent.