All they really need is the hard drive to do the analysis they need to perform. If you do not wish to file a conversion action or replevin action (recovery of personal property) then have your attorney contact the Sheriff's department and District Attorney to arrange they return the items they do not need for their investigation.
It is not an ideal situation, but realistically speaking if you buy a new hard drive and ask them to transfer your business files to the new hard drive and then return the rest of your computer equipment they can hardly complain. Again, while you shouldn't have to pay this expense it may be the quickest, cheapest, and simplest method to get your property back and your business up and running.
Another option would be for your attorney to ask them to make a mirror image of the hard drive and return the property pending their investigation. They may be unwilling to do this until they've confirmed an absence of illicit images, but it does not hurt to ask. Further, if your attorney communicates the urgency of getting your business computer returned they may be able to expedite the examinations they need to conduct.
Please reply if I can help further.
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