I admit I'm a bit out of my technological depth here so this may be an obvious question but does a master node maintain anonymity?
A follow-up question if the answer is 'no': Could there be grounds for the prosecution of a master node operator for money laundering?
Behind TOR, yes.
As for your second question, mixing coins is not money laundering as far as I know, it's a privacy tool.
Ah ok, thanks. If the first question is resolved, the second doesn't really matter.
I was imagining that the issue could be with a legal system (in any country) defining "coin-mixing" as a money laundering tool. The master node operator is obscuring the transfer of money from one place to another. I'm not sure that saying "you can't prove that illegal money passed through my node" will convince a judge.
I'm going to quote myself because I did a double edit the same time you did your post.
double edit:
Going by this:
http://uknowledge.uky.edu/cgi/viewcontent.cgi?article=1027&context=law_facpub1) You would have to provide the service knowing that the other party was structuring/laundering (you wouldn't).
2) They would have to be able to prove through tracing many DarkSends that those parties even owned the coins. Next to impossible unless sybil attack somehow happens on a wide scale (highly unlikely from what I've read by Evan).
3) Most of those sections have to do with a user declaring their own money or a receiving business declaring the money, both of which would not apply to a master node.