In nearly all cases the account holder cannot be 100% confirmed as the person using the internet service to torrent with, iinet are correct in stating that any release of customer data will lead to speculative invoicing or harassment aimed at pressurising the account holder to act as an unpaid investigator, this will involve litigation after all so any requests aimed at the account holder for information must be replied to with a scale of charges so the account holders time is paid for., this is standard legal practice.
At this time enquiries should also be made to iinet to ascertain how long they store such data for and also some statistical data obtained from them regarding just how accurate is the equipment used to generate the data as in some other countries is has been shown that this type of customer billing data can be incorrect and thus this too is an important avenue to investigate to prevent a potential miscarriage of justice.