It's not absolute, but we have something called the "American bystander rule." (pdf file) In the United States in general, we do not have have a legal duty to intervene if someone else is in danger (regardless of whatever moral duty we might or might not have). Would we be better served with something like the Good Samaritan rule in Europe and some jurisdictions here that requires intervention, at least of the level of reporting a crime?
In the wake of the gang rape of a 15-year-old girl outside a California high school, some are questioning Indiana's lack of laws requiring bystanders to report serious crimes.
[. . .]
Indiana does have laws requiring people report child or elderly abuse.
State Rep. Vanessa Summers said she wants to investigate the issue further and discuss the possibility of expanding the law to include other serious crimes.
I have mixed feelings. I can see a lot of reasons not to require actual intervention, but reporing a crime seems like basic citizenship, i.e. doing for others in trouble what I would want them to do for me if I were in trouble. On the other hand, I can see problems in enforcing such a law, which would make it tough to apply uniformly.
What do you think?
