A Sotapanna would act exactly the same a law-abiding, normal person would act.
The key is think about what kind of mental factors are likely to arise in such a person acting as a “good samaritan” or a “good neighbor”.
How can dosa arise in such a person who is trying to prevent a wrong doing? Law-breaking is almost always immoral. Preventing that is a good thing. Of course, there are limits to one can do. At least notifying the appropriate authorities can be done.