OT?: Legal question about p2p

[Erik Bixby]

Does anyone here have any idea what degree of certainty organizations
such as the RIAA must have in order to subpoena people?  I had an idea
for a scheme of exchanging files where the peers protect each other
from knowing for certain whether or not a particular machine actually
holds any particular file.  (http://www.crabboy.com/secure.txt)=20
However, if it is the case that even if there is only a one percent
chance the RIAA can still subpoena people, the scheme would only serve
to run up their legal costs.  Not a altogether bad thing.  But, I was
hoping that there was some sort of legal threshold they had to meet...

Thank you, in advance, for your time.
-Erik