I am not sure why your chain of command would tell you that your case would remain open for 5 years. I know of no reason that this would occur and do not believe it is possible if the case was closed favorably. Perhaps they were simply referring to the titling process. Here is an explanation of the titling process.
C.I.D. will not leave the investigation open for five years. If this was the case, the Soldier would have to be flagged and would not be able to reenlist.
What they may be talking about is C.I.D. probably “Titled” the Soldier during their investigation. This means that they named the Soldier as a suspect on a Report of Investigation (ROI).
If the Soldier was titled, it will follow this Soldier for the rest of his life. From what I understand, you do not get removed from this database once in it. So, anytime he applies for a government job, police, security, basically any job where they do a background check, this issue will come up.
I found the following recent article which explains the basics of the titling process.
I was MPI attached to the CID office working dope. Titling is required according to DOD Instructions (formal policy) when there is “credible evidence to lead a trained investigator to believe a crime occurred.” This does not require SJA approval. This is an operational decision made by either the Provost Marshal (for any case which they are the investigating authority) or the CID Office. The decision to title a soldier is ultimately the responsibility of the CID Special Agent in Charge, typically a CW3/4. The PM/investigator will coordinate with SJA for an opine.
What probably happened to you is you were under investigation and the case was unfounded. All unfounded cases will still show up for a Military Police Records Check that you were listed as a subject of an unfounded investigation. It will clearly state it was unfounded but could still have adverse effects on things such as your spouse wanting to have an at home day care. However it is specifically marked UNFOUNDED
They will show up for 5 years before they are purged from COPS* and it is the SAC/PM/INvestigator (PM/SAC depending on if it is an MP case or CID Case)