Let’s take the military, for example. Soldiers are actually paid to kill each other.

Yes, I know that’s not the same. Legally the killing of an enemy in the heat of war is allowed. It’s fine to kill people if it’s for the right reasons. If you’re defending your country, you can actually get a medal for it.

And what about the death penalty? In Britain, it was abolished in 1965, though treason remained punishable by death until 1998. But across the Pond, Texans are happy to stick the needle in the arm of anyone who looks at them funny. They call it justice.

My point is: sometimes killing people is a heinous crime, and sometimes it’s the right thing to do.

And the line between the two is much more blurred than you might think.

Murder one or manslaughter?

Second-degree murder or self-defence?

The Americans have a legal defence they call the ‘castle doctrine’ which is actually based on English common law: your home is your castle and you have the right to defend it. You don’t even have to prove you’re in danger at the time: if your drunk neighbour breaks into your garage one night to take back some tools he lent you, you’ve every right to shoot him in the back.

Seriously, is it any wonder people like me get so confused?

We don’t have an instinct for right and wrong, remember. We have to learn your rules, and the goalposts are constantly shifting.

So you tell me: when is it OK to take a single life to save many?

If the ‘single life’ in question is a teenage boy wielding an AR-15 assault rifle in a primary school, taking him out is a no-brainer.

But what if he hadn’t yet picked up the gun?

What if he hadn’t even bought it?

Suppose you’ve known him since he was a kid. A neighbour’s boy, maybe, or your nephew.

Say you’d found him trying to drown a kitten when he was seven years old. A year later, he attempts to strangle his little brother.

His mother doesn’t want to hear it: says you’re making something out of nothing. It’s just roughhousing, she says. Boys being boys.

So you keep a quiet eye on him. And one day you find a notebook he’s filled with images and descriptions of the horrific things he’d like to do to people.

A kill book.

He hasn’t actually done anything criminal. Not yet.

No one can see who he really is, except you. But you recognise the darkness in him. You know, you know, this boy will kill sooner or later.

Ask yourself: if you’d been in my shoes, what would you have done?

chapter 20

millie