For a definitive answer I would refer Bazile to the work of Darley and Latane (1968), and the earlier Berschied and Walster (1967). Irving, Piliavin et al (1969) contributed valuable insights too. All based their work on the murder of Kitty Genovese in Queens (New York). Many factors influence the 'Good Samaritan' response, both positive and negative. It all depends...
Coincidentally, a news item in today's D. Telegraph tells of an aging man who was pepper-sprayed, arrested and spent several hours in police custody when he attempted to intervene in a knife attack on a 3rd. person. This Good Samaritan did not even receive a police apology when he was eventually released. There is a moral there somewhere.