If your research is likely to uncover evidence of illegal activity, even if you are not directly studying the illegal activity, your ethics application will need to be reviewed by the full Human Research Ethics Committee (HREC).
You should inform participants upfront of the risks inherent in this kind of research. If illegal activity is uncovered, there could be legal and social implications for you and for your participants. In addition, you need to consider the possibility that you as the researcher might have an obligation to share some research information, for example under mandatory reporting obligations or if your research is subpoenaed.
Before submitting your protocol, please carefully read Chapter 4.6 of the National Statement and contact the Ethics Office or the Legal Office if you have concerns.