As every law student knows, the longstanding rule in the US has always been that, subject to very few exceptions, there is no duty to help someone in need of help. In other words, there can be no liability for failing to help someone even if their life depends on it. The rule has been severely criticized over the years but it is still generally accepted and applied.
As I am sure you have heard by now, a few days ago a man pushed another man onto the tracks of the NY City subway and no one came to his aid. He was killed by a train while bystanders watched and at least one photographer took pictures. The incident has generated a new discussion as to whether the people watching should have helped. Much of the attention has been expressed as outrage at the photographer who decided to snap a few shots rather than to do something for the victim who was in danger and struggling for his life.
Yet, it is unlikely that the incident will result in any changes in the law. Courts have always been reluctant to impose a duty to help for a number of reasons. First, it is difficult to draw a line between a moral duty and a legal one. Second, it is generally thought that it might actually be better to discourage people from helping unless they know what they are doing (ie, have training to intervene) for fear that in trying to help, people might make things worse. Good Samaritan laws are usually enacted to encourage those with training to intervene in emergency situations to do so when they are not obligated to do so. Finally, Courts are reluctant to impose a blanket duty in all cases because it might force those who would have the duty to help to place themselves in dander. No one wants to force people to help if doing so will put them in danger.
For a good discussion of the subject go to Prof. Jonathan Turley's blog here and the NY Personal Injury Law Blog here.