People watched as a man raped woman on a running train in Philadelphia

Spectators did nothing when a stranger raped a woman on a train near Philadelphia last week, police said. Fiston Ngoy, 35, is charged with rape, sexual assault, aggravated assault, and several other charges after an employee of the South-East Pennsylvania Transportation Department reported that "something is not right" with a woman in the train and called the police. But people on the train 'witnessed this heinous act' and did not call 911, a transport authority said.

The video from the train camera shows Ngoy trying to touch the victim as she tries to force him away, the prosecutors stated. Ngoy then pushed her down, torn off her clothes and attacked her. According to authorities, the assault lasted eight minutes.

"I'm upset about those who did nothing to help this woman," Upper Darby Township Police Department superintendent Timothy Bernhardt said over the weekend, according to the New York Times. Anyone who has been on the train should look in the mirror and ask why they did not intervene or why they did not do something.

But the 'bystander effect' is far from unusual. "The larger a group is, the less likely people are to intervene and take action," said Heather Hensman Kettrey, an assistant professor at Clemson University, who studied the bystander effect and ways to train people to counteract it. "People tend to think someone else is going to do something."

"The problem is that when everyone thinks about it, nobody does anything," she said.

Ana Bridges, a psychology professor at the University of Arkansas who studied the bystander effect, said four conditions must be met for a bystander to intervene.

People should have understood that something is wrong, confirmed that what is going on is a crime, decided that they have a duty to prevent it, and definitely acknowledged that they have the necessary tools to do so.

The concept of the effect has its origins in another story of sexual assault — that of Kitty Genovese, a 28-year-old bartender who was raped and robbed in 1964 in front of her apartment building in Queens, New York. Her neighbours did nothing to stop it, although recent research has revealed that parts of the Genoese story are apocryphal.