But one became much more notorious than the others.
Not because of the victim, or because of the killer.
But because of the behaviour of the witnesses.
It happened around 3am. Kitty Genovese was coming home from her job.
She lived in a block of flats, surrounded by other blocks of flats.
As she parked her car and walked to the entrance, a man came up behind her and started stabbing her.
Kitty screamed for help.
Lights came on and people looked out of their windows.
Thirty-seven people heard her screaming.
But no-one did anything.
One man opened a window and shouted: "Leave that girl alone."
Kitty’s attacker ran off.
But no-one did anything.
So, ten minutes later, the attacker came back.
By now, Kitty had crawled to the entrance of her block.
The attacker resumed stabbing her, and Kitty resumed screaming.
But still no-one did anything.
So he raped her, and still no-one did anything.
So he went through her bag and took her money.
And still no-one did anything.
When he had no more use for Kitty, he left her dying on the floor.
Eventually, an hour later, someone called the police.
Kitty died in the ambulance.
What shocked everyone was the behaviour of the witnesses.
It became a cliché around New York City.
"I didn’t want to get involved."
But, for me, the more useful insight is something else one of the witnesses said.
She said: "Everyone heard it, so we thought someone else would call the police."
It’s called "the bystander effect".
If we want people to act on what we say, we have to talk to them as individuals. Not a mass broadcast addressing thousands
Basically, the more people who witness an event, the less likely a single person is to respond.
When we are the only witness, the responsibility is totally down to us.
But if there are two of us who witness it, our responsibility is halved.
If there are ten of us, our responsibility is only a tenth.
Our importance is diminished by being a small part of a greater mass.
We’re off the hook.
Which is what happened that night in New York.
Everyone thought someone else would do something.
So no-one did anything.
For me, it shows the power of individual communication and the weakness of mass communication.
If we want people to act on what we say, we have to talk to them as individuals.
Not a mass broadcast addressing thousands of people.
It’s a natural response.
If you’re talking directly to me, I have to listen.
But if I’m just part of a crowd, if you’re just addressing a mass of people, I don’t have to pay attention.
That’s what the great orators, and the great communicators, have always known.
Whatever the media, we have to hold it in our head that we’re only talking to one person.
Even if we’re actually talking to millions.