I trust you guys, but are acting extremely unprofessional. I will personally never use your service in fear of you publicly going after users in this format. From an outsiders perspective you really look terrible. I'm serious. ZT looks bad, but so do you.
You have stated ZT is the prime suspect? In what? Is there even a fucking police report? He is the prime suspect according to you, AFAIK.
Basically, you are just holding his money because you want to. You have stated he has broken your TOS. I am sure you have violated your own TOS when you have posted personal information about your users all over the web.
This is turning into a big fucking joke.
Get the fucking money to the lawyers so us bitcoinica users can get our money back. That's it.
Say what you will but if Roberto and Mark hadn't done this, we would be no further towards recovering funds. So far Zhou has managed to transfer 15k BTC out of 20k BTC and 140k USD promised.
If anything you should be thanking AurumXchange and MTGox for getting to the bottom of this.