This theory was first put forth in a famous 1968 study by Darley and Latane, who were intrigued by the seemingly apathetic reaction to the murder of Kitty Genovese.  
The original experiment to confirm it included scenarios dealing with the theft of beer in a store, an epileptic seizure, and a smoke-filled room.  Along with the Caporeal Dilemma it is considered the most prominent example of social loafing.  This theory was first put forth in a famous 1968 study by Darley and Latane, who were intrigued by the seemingly apathetic reaction to the murder of Kitty Genovese.  FTP, name this psychological phenomenon in which individuals, in the presence of a group, are less likely to help a person in trouble.
The original experiment to confirm it included scenarios dealing with the theft of beer in a store, an epileptic seizure, and a smoke-filled room.  
bystander effect