Confidentiality for research participants when crime occurs
The fact that there was no law to protect social scientist researchers meant that if the police were investigating a crime the research notes could be taken subject to a court order, or Venkatesh would face jail himself if he failed to hand them over.
Reporting illegal activity is on a continuum. At one end is a situation where you would have a moral and legal obligation to report the activity, generally if there is a serious and imminent risk of harm to either the individual concerned or others (planning a drive-by shooting would certainly fall into this category). At the other end is crime with no external victim e.g. information about personal drug use, here the responsibility is to keep this information confidential. If you are investigating information about illegal behaviour as part of your research the advice would be to ensure anonymity of participants in your research notes. It would not usually be expected that these participants would sign informed consent forms.