If it's really 700k+ BTC ($350M or so) it'll be interesting to see how many years an investigation goes on for. Every txid is public so eventually someone somewhere will do something stupid, and so it will begin, one of the best episodes of non-fiction real-life drama you've seen yet.
Gox should be able to identify every double withdrawal transaction they ever made, and they have IDs of all these customers.
They said:
1: Double spend going on for [several] years
2: From unverified accounts
Yeah, it's basically like a bag of pus that exploded. I mean they could have been honest long before running their stupid inflated 1000 price, I mean everyone wondered wtf are they doing? Now it's clear. I mean deleting the website and twitter feed? It's like CLANK the ass end just dropped right out.
Lawyers will save the world! Yay! Go get em boys!