If Cryptopia's management was actually behind this hack, they'd not be cooperating with the police at this time due to fear of being jailed. I still think that Cryptopia's bad security caused this hack, not the Cryptopia's bad intentions.
The question I have is:
how many such cases that some hacker stole funds from some exchange and was caught and recovered the funds?
I do not know the statistics, but I know that I do not see every day the news channels say they found the hacker X and recovered the funds of some exchange that was targeted by hackers. following this logic, they may have stolen themselves because they know there are few chances of being caught by the police.