[willy]

Sorry Builder, there is walking sh!t everywhere, there always has.
Follow the advise and get the items reported with a serial and model number along with any owner applied number you may have done.
If they are seized somewhere the PD where it is seized will do a NCIC or SCIC check on the items and if they are not entered correctly they will be auctioned off somewhere or destroyed.
The person who came to your house is the governments way of saving money and not hiring enough cops to do the job. All they want is a report number to justify their existance and to provide a number for insurance purposes.
There will be no investigation as there should be and no evidence recovered to tie a perp to a crime.
If you want that sounds like you need to do the checking around yourself. Likely from the sound of it you are right about a inside job of some kind. But a couple of things to think about, whoever did it cqme in prepared, in the dark and new how to cut it out without spending much time and making any noise.
Sounds like an experienced mariner or someone who grew up around it and done the work themselves. Thats a pretty clean cut for a normal thief. JMHO

Oh yea, talk with the people who sold you the units and/or the install, find out if anyone else had thefts, might ring a bell with them. Unless it is a small operation with one or three employees, in that case just kind of show up and look around.