The two cases that have set off the debate had very different outcomes. In one, German-Turkish student Tugce Albayrak died after she tried to help two teen girls who were being harassed by several men in the bathroom of a McDonald's in the German town of Offenbach. Albayrak was hit on the head and knocked to the ground by one of the suspected harassers in the parking lot of the restaurant and died later in hospital.
In the other case, two sisters in India fought back against men who had been harassing them on a bus in Rohtak. One of the sisters told BBC News that the two began physically defending themselves and beating the men with a belt after they saw none of the other passengers were willing to intervene to help them.
We look at some other cases where bystanders have intervened — with mixed results.
Hammer attack, October 2014: William Yee of Langley, B.C., was hit on the head with a hammer after trying to help a woman who was being robbed on the street at gunpoint. As Yee approached the robbers, one of them held a gun to his head while the other hit him with a hammer and kicked him. Yee lost consciousness for a moment, and when he awoke, his attacker continued to hit him with the hammer and kick him.
High school stabbing, September 2014: High school student Hamid Aminzada, 19, was stabbed in the stomach and slashed in the face after trying to break up a fight between two students in the halls of North Albion Collegiate Institute in Toronto. He died of his injuries in hospital. A 17-year-old fellow student was charged with second-degree murder in his death.
Good deed gone bad, April 2014: A Good Samaritan who stopped to help the driver of a vehicle she saw had crashed on the Hanlon Expressway near Guelph, Ont., was rewarded for her trouble by having her own vehicle stolen by the driver she tried to help, who had stolen the first car moments moments before he crashed it. The woman's vehicle was eventually recovered and the man arrested.
Bus stabbing, April 2013: Two Good Samaritanshelped save the life of a New Brunswick bus driver who was stabbed multiple times by a passenger as he was pulling his bus into a station in Perth-Andover, N.B. One of the seven passengers on board noticed what was happening and grabbed the attacker by the shoulder and told him to stop. The attacker was startled and took off. A man who was at a nearby convenience store at the time gave first aid to the wounded driver and tried to staunch the loss of blood before the ambulance arrived. The driver later credited both men with helping keep him alive.
Pumpkin theft, October 2011: A 57-year-old man died of severe head trauma after he tried to dissuade two teens from stealing a pumpkin from a display outside a closed IGA store in Gatineau, Que. Paul Hines was cycling by the store with his wife when they spotted the young men. The Hineses confronted the teens, and things became heated. One of the two punched Hines, knocking him to the ground. He fell into a coma and died a week later. An autopsy showed he died from the trauma sustained when his head hit the concrete.
Stanley Cup riots, June 2011: Robert Mackay survived after being swarmed and beaten by a mob of rioters after he tried to prevent them from looting a Hudson's Bay department store in downtown Vancouver after the Canucks lost the final game of the Stanley Cup playoffs. Internet video from that night shows a number of people kicking and punching Mackay, dragging him to the ground and dousing him with pepper spray. Five people were convicted of assault and other offences in connection with the attack.
Laptop thief, May 2011: A posse of Twitter users helped Sean Power of Ottawa track down his stolen laptop in New York after he used a program called Prey to trace the thief's movements and tweeted about it. Two people who saw the tweets went to the Manhattan bar where the thief was spotted and confronted the man. They put him on the phone with the laptop owner, and he agreed to return the computer. At the time, Power said he had urged the Twitter vigilantes to not confront the thief: "I completely disavow that kind of action in this kind of scenario. It's super, super dangerous," he said.
Bystander effect, April 2010: A Good Samaritan in New York who tried to help a woman being threatened by a knife-wielding man was stabbed by the attacker and bled to death on the sidewalk. More than 25 people passed by Hugo Alfredo Tale-Yax as he lay bleeding for an hour and 20 minutes, with one person even taking a cellphone photo and another rolling him over but not doing anything to help. By the time paramedics arrived, he was dead. The incident is often used as an example of the bystander effect, where onlookers fail to act assuming others will do it or resist intervening until they see someone else doing something.
Highway abduction, July 2009: A Calgary couple were caught up in a violent confrontation that could have ended badly when they intervened to rescue a woman struggling to get away from a man who had her pinned on the ground at a roadside stop on Highway 817, east of Calgary. The woman broke free and managed to get into the couple's Jeep as they called 911, but her attacker pursued the vehicle and eventually crashed his car into it. Police arrived in time to rescue the three and arrested the man at gunpoint.