OK...
times like this we all think "never destroy evidence, it should be kept etc etc" (for future analysis, advancements in technology blah blah blah.
Now, there are a couple of hundred murders per year, more serious crimes, and all sorts of terrorist investigations and the like...
On a practical level, there's a LOT of stuff to store. A lot of paperwork to file (or digitise), tapes, dna, prints, bullets, weapons, clothes, furniture! cars!....
Where the hell is it all going to be stored?
And who's going to pay for it?
I sound like I'm being facetious, but it's a serious question and consideration.
Do you want to pay more money in taxes for it? or give up some countryside to house it all in specialist warehouses / controlled environments?
How long should we keep it?
What about bodies?