TLIK: Potential examples of mesora is reporting to, say, the police or to ACS (CPS). Lack of arrest does not make it not a mesora case, if the net result is the entity (police, CPS, etc.) will stick governmental power, even outside of detention or seizure of children, to make Jewish family lives miserable.
Suspicion of a crime that lacks knowledge thereof, does not permit disregarding the halachos of mesira.
At the very core, when the local non-Jewish laws mandate reporting (i.e. a mandated reporter) in insurances where the halachos of mesira are applicable and prohibit reporting, a Jew is bound by the halacha even though the secular law is otherwise.