Chen stole Zhou's identity. Used it for credit card fraud and steal money from Bitcoinica. Australian police would suffice, Zhou resided there during the theft.
And whatever you just wrote above directly applies to Zhou, he claimed that he got funds back from Chen by threatening with Chinese police.
As of right now Zhou is black mailing.
That being the case, can ZT give us some indication as to why you've not gone to the Australian police? (If your reasons would make you vulnerable to the angry mob you could at least acknowledge the question).
Agreed that police involvement would appear to scare 'Chen' into co-operating. It's actually also part of the reason why I have doubts as to whether Chen exists. That being said, I believe ZT has additional leverage on Chen (e.g. knowing other information on him/family). It's fair to say there's very little info here and what there is could conceivably be made up (i.e. Chen doesn't exist).