@Linkat,
Linkat wrote:To what extent are witnesses responsible? Should they be legally responsible? Should they be morally responsible?
In the US, bystanders have no legal responsibility to assist those in need unless there is some prior duty to that person. For instance, a parent will have a legal duty to assist his or her child, a police officer has a legal duty to assist anyone, etc. In addition, a person who, by his/her actions, creates a situation where a duty can be assumed in law also has a responsibility to render assistance. For instance, if Abel places Baker in a position of great danger, then Abel is obligated to assist Baker in avoiding that danger. Ordinarily, however, no one has a legal duty to assist anyone else. That may not be the law in other countries, but it has always been the law in the US.
Whether the subway workers in this particular case had a duty to assist the rape victim depends on whether people in the position of those workers have a pre-existing legal duty to assist subway riders who are the victims of a criminal assault. My guess is that they don't. They probably have a duty to call for assistance (which they did), but they don't have an obligation to become actively involved in fending off the attacker.
As for a moral duty on the part of the subway workers to intervene, that all depends on what version of morality you're talking about. Personally, I doubt very much that the circumstances, as you've set them forth, would have morally required intervention by the subway workers above and beyond what they actually did.