I wonder how corrupt law enforcement is, where OP lives. Theoretically they could have a safe meeting room inside the station & let the data recovery business be done there, then OP would split the ₿ between the watch-only addresses of their own & the data recovery person. Then after confirmation, both could be allowed to leave, and neither could rob each other immediately - they'd have to figure out where the private keys to the watch-only addresses are. Also, in case the data recovery fails, OP would pay them cash for their effort, which was double-counted & put in an envelope to the side before anything else.
There are data recovery services that, for a fee, allow the client to be present during the data recovery process, so I advise the OP, if he is telling the truth, to look for one and try to save his lost treasure.
I went to an Apple Store to have my computer's firmware password removed (had ownership paperwork & the root/only user password - but wanted to reformat the HD & put Linux on it for Blockstream satellite reception) & they refused to let me be present, would only take in the back, and get back to me sometime when it was done. Needless to say, I walked right back out with the computer.