Daniel Finkelstein considers a well-worn phrase:

Between 2003-2008, I found more than 200 different murderers or murder victims who were described by their neighbours as “keeping themselves to themselves.”

Several examples are quoted, including this rather infamous one:

In the dark, someone was at the stank, pulling masses of rotting flesh from the drains, slopping them into black bag after black bag. It was their neighbour Dennis Nilsen. A civil servant who kept himself to himself.

But why is this not entirely helpful phrase deployed so readily?

There are two possible explanations for this. The first is that people who keep themselves to themselves are substantially more likely to be murdered or murderers than other members of the population. I suppose this is possible. But I did note that there were more than 50 footballers who were also described as keeping themselves to themselves in training. This – and the fact that the phrase appears to be British and isn’t used to describe for instance American murderers or murder victims – leads me to the second explanation.

This is that we all copy each other when asked to provide descriptions by the media. The political scientist James Stimson notes that opinion pollsters frequently get people to opine on issues they don’t actually have an opinion about. He calls these fake opinions “non-attitudes.” I suspect “he kept himself to himself” is the crime equivalent of a non-attitude. The neighbour doesn’t actually know anything. Although perhaps their ignorance is caused by the murderer or murder victim actually keeping themselves to themselves.