With how far the police department seem to be going out of their way to fabricate a case against you, it seems like it might be best to assume that whatever materials of yours that they still have are lost to you. Even if you do eventually get anything back, it might not be usable, either because of mistreatment of your things or just age, because it's sounding like this investigation can take as long as the police want it to take whether it's justified or not. Whatever that would mean for your plans for work, it might be better to start planning for that outcome both mentally and practically.
I get that this is a huge loss of years worth of work. It's a catastrophic blow to your business. But I think from a mental health perspective and a work flow perspective, it would be more productive to just assume that you'll never see that data again and decide how you'd want to proceed from there and start working in that direction. In business relationships, it sometimes happens that you end up in situations like this where a business partner/client/supplier/whatever is kinda holding your project(s) hostage by not delivering what you need when you need it and not telling you when it will be delivered. It will be more stressful, time consuming, and expensive to operate your business according to someone else's uncommunicated timeline than to cut your losses and assume you won't be able to get what you were supposed to get from them at all and either replan your projects around that assumption, or even just write off the projects as losses and move on to new ones.
This has clearly been a traumatising ordeal. I think deciding how you and your business will move forward for yourself on your own terms, rather than at the whim of all those other people and groups that have shown no consideration for your wellbeing, will help you start to get back to your normal life again, despite still being embroiled in these horrible circumstances
