Do what is appropriate under local laws and company policies. Granted, you are in Australia where the laws will differ from ours...
In the US: (1) possessing "underage", i.e. child, pornography is a crime; (2) it would be appropriate for the employer to discipline (suspend or fire) an employee for policy violations, assuming there is a business-use-only policy for company equipment and internet usage, (3) the employer should present evidence of criminal acts to the police (you said that as part of your duties, you have legitimate access to what you found), because (4) knowingly witholding evidence of criminal activity from the authorities may make the company--and you!--liable for enabling the criminal acts to continue.
Give your findings to the company management, so they can take appropriate action. Forget about Bethel and the branches, it's time for this hypocrite to "Render unto to Caesar"!