What can i do if a detective failed to release my property (firearm)

You may file a motion with the court that was assigned to your case -- asking for a court order to have your property released to you.  Since this may not be as simple as it sounds, I recommend retaining an attorney to handle this for you.  Since the alleged criminal incident was in 2016, it is possible that it is too late to get your property back -- but you could try. The other possibility is to contact the prosecutor, tell him/her you want your property returned since the case was resolved without a conviction, and ask the prosecutor to contact the detective to make arrangements for the return of your property to you (assuming, again, that it is not too late).   Caution -- even though you were not convicted, it is very risky (in my opinion) for a defendant (even if the case is over) to directly communicate with the prosecutor.  The prosecutor could use the contact as a way to try to get more information and potential evidence -- without you realizing it.  Depending on what new information the prosecutor gets -- and other factors such as statutes of limitations, there could be potential for re-filing charges, or filing new charges, against you.  Consequently, I recommend contacting an attorney to handle this for you.  I would not be able to help you becfause I do not handle cases in Pinellas County.