It is not likely that you would be arrested months after the incident but you certainly could be "charged". If the police took your name and other identifying information and they had personal knowledge of you being a minor in possession of alcohol, they have at least a year (maybe longer, I didn't look up the statute of limitations for minor in possession cases) during which they can file an application for criminal complaint in court. Or they could file something with the college student discipline committee.
With them saying "in the next few months" it doesn't seem likely though. To me that sounds more like a "don't do it again or else" kind of thing. I suspect that what they wanted was the name of the person who bought the alcohol for you, brought it onto campus or gave you the fake id that let you purchase your own. You might want to talk to a local criminal defense attorney about whether you should take any next steps with the police or just stay out of trouble and hope the police do not do anything other than keeping your name on file.
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You could be charged some months later, although if there is a significant delay in the time between the incident and the issuance of the complaint against you, the complaint is vulnerable to a motion to dismiss on due process grounds. Unlike say a traffic violation, it is not necessary to issue you a citation on the incident date in order to charge you later on.
If you are charged with this misdemeanor offense, you will have a right to a clerk's hearing before any criminal complaint against you is issued. You will be notified by mail of any upcoming clerk's hearing. If you have no prior record, it is very likely that the clerk will not issue any criminal complaint against you. Note that a conviction for minor in possession is a fine of not more than $50 for a first offense and a 90 day loss of driver's license. There are many dispositions short of a conviction, however, that do not trigger the fine and the loss of license.
If you do receive a notice of an upcoming clerk's hearing, retain an attorney immediately and he will help prepare to obtain a favorable result at the clerk's hearing.
Dominic Pang (617-538-1127)
Disclaimer: This answer is provided for informational purposes only and it is not intended as legal advice. Additionally, this answer does not create an attorney-client relationship. If you wish to obtain legal advice specific to your case, please consult with a local attorney.
I agree with my colleagues -- you cannot be arrested on this type of offense after the fact, but they can seek the issuance of a complaint. For this type of offense, the clerk-magistrate would be unlikely to issue a complaint without a hearing, at which the police would have to prove there was probable cause as to each element of the offense (minor, possession, alcohol). Each of these would be difficult for them, so long after the fact. In all likelihood, the complaint would not issue.
If it did, you would be well advised NOT to plead guilty, or even "admit to sufficient facts". If you are ever charged (very unlikely) consult a lawyer. You are probably not entitled to a public defender.
You don't say whether it was campus or town cops. If the latter, and if you are charged, it might be suitable to inquire as to what gave them the right to come on campus, into the dorm, etc. If the former, they may or may not have had the ability to arrest you. Some campus cops have no more right to arrest you than any other citizen, which is no right at all for a misdemeanor. (If they were armed, they probably were "peace officers", with the ability to arrest for a misdemeanor committed in their presence, if not armed, they may not have been peace officers).
In the mean time, keep your nose clean. The City of Boston is now considering non-convicted criminal history re employment applications (In my opinion, un-Constitutional).
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