I would use email so you have a written record. When the municipal court violated open records I sent an email to all of the administrators, mayor, and city council members. I now have written proof that they condoned a violation of my civil rights. If you want to follow up with a phone call, fine.
Further thought - you gave up possession voluntarily. You should try to contact the officer and tell him you want your computer back.
Then if he says no, put it in writing that you are revoking that permission and want your property back.
Then go to the P.D. , ask for the senior officer in command. Give him a written request for the return of your property. If he says no - then ask him for a copy of the grievance procedures in writing.
If it is going to interfere with your work make that the justification for IMMEDIATE return of your property.
Don't go to anyone else - including a lawyer - until you've tried this, and you can do it today. Play the co-operative citizen but make it clear that you were intimidated and confused and made a big mistake in surrendering your property.
They may say they need it for an investigation.
Do you have sensitive personal info on the hard drive you don't want them to see?
If not I would offer to give them the hard drive after you buy a new one and back up your personal info.
You have gotten yourself into a box, I'm not sure how you're going to get out of it.
They didn't take your computer - you gave it to them.
Warning - this is free advice, you have to realize that I am not a professional, just another victim. Consider everything you are told here and do what you think is right.