There are some real-life lessons to take from this; for example if you or someone else is having a medical emergency such as a heart attack on a busy street, do not simply call out to the crowd, "Someone call an ambulance." Instead, single out one specific person nearby and point to him or her directly and say, "You, call an ambulance!" or "You, help me stop the bleeding."
Research shows that this is far more effective and is much more likely to result in immediate and decisive action. It's not that people are indifferent, cruel or lazy; it's that without a specific, clear, immediate request, people are much more likely to assume someone else will take care of it. Parents can also use this phenomenon to their advantage, by for example assigning specific responsibility to one child instead of telling a group of kids, "I want this mess cleaned up by the time I get back."
Interestingly, Hernandez's sister Norma claims that she did in fact tell New Jersey police that her brother told her he killed a child 25 years ago, but nothing was ever done. Her claim has not been confirmed, but assuming it's true, what would make his own sister turn him in when dozens of strangers didn't? For one thing, he told her in person and in private.