Yes, assuming that the investigation is over, you should be able to get your computer back. You can start by making a formal written request to the department for the return of your computer. If that fails you will probably need to retain an attorney to start an action in replevin. This is essentially a lawsuit in which a person claims someone else is wrongfully, or unlawfully, holding property that belongs to someone else.
The police department have a limited right to retain private property during the investigation of a crime. Unfortunately because there is no statute of limitations on murder in Maryland, they can technically hold on to your computer if the investigation is still ongoing. The Maryland State Police, as well as the local Sheriff's and Police Departments have written policies for the return of evidence in cases. A letter will not do. You need to fill out the specific form each department has and it must be approved by the chain of command. A Replevin action may be filed, but it will be hard to prevail unless you have proof that the piece of evidence (your computer) is of no evidentiary value to the investigation any more, or that the investigation does not need your property to be completed. Another factor to consider is how the computer was seized. I recently handled a Replevin action following a search and seizure in a warrant. Very complicated process. Consult with a Maryland licensed attorney before writing any letters or filling any forms on your own.