The suspect in a recent brutal beating of a New Jersey mother in front of her two year old son turned herself in to police Monday.
Latia Harris, 25, faces a litany of charges, but one question remains: why didn't bystanders try to stop the assault?
"The more people there are, the less likely they are to act," forensic psychologist Robert Gordon said.
Psychologists call it the 'bystander effect' or 'diffusion of responsibility.'
"Gee no one is acting maybe someone else will do it. Maybe I shouldn't get involved, maybe there is a reason not to," Gordon explained.
Camera phones and social media only exacerbate the problem. Gordon says they act as a filter, taking the user out of the real life situation.
"It interferes with what we call the person-to-person relationship. It becomes a person-to-it relationship. Then it becomes something that is a news story or something that I get status for," Gordon went on to say.
This isn't new.
The psychological phenomenon was thrust into the national spotlight following the 1964 brutal murder of Kitty Genovese.
The 29 year old was stabbed repeatedly near her Queens, New York apartment with neighbors looking on.
No one helped and Genovese died.
In that case or in this one, Gordon says all it takes is for one person to act.
"It's a signal to everyone to say, 'Wait a second. This is a human being. They are being treated badly and abused. I'm not going to stand for it.' It takes just one person," he said.
Police say no witnesses will be charged for not helping in the beating in Salem, New Jersey.
Allentown, PA 18102