Whodunit?

I was watching a 'whodunit' on the TV tonight.
It was a mixture of Dr Who, Agatha Christie, and Cluedo.

It was quite entertaining, although not as scary as some episodes!

Anyway, it made me think about why we want to know who dun it?

After all, the bad thing already happened.
We can't undo it.

Is it about punishment?
Or prevention?
Or revenge?

In an ideal world no-one would do wrong.

But we don't live in an ideal world.
People die all the time.

How much are we responsible?