On a winter's night in 1974, a crime took place that would obsess the nation.

It was an extraordinary news story.

The story of an aristocrat, Lord Lucan, who's said to have killed the family Nanny,

mistaking her for his wife, then somehow just disappeared.

One of the great mysteries in English criminal history. We're still looking for

Lucan. It's honestly one of the most powerful stories of my lifetime. I'm Alex Fontunzelman.

This is The Lucan Obsession. Listen on BBC Sounds.

So it just arrived in Norwich and we've got an address for Fox and we're going to try and see if we can see where there's any signs of life there.

So far, we've heard Daniel and Rodrigo's account of what happened, we've heard from the Brazilian police and from from Fox's colleague, Robert Delbos.

But we also want to know what Fox has to say.

Thanks to our colleague Guyoum, the social media sleuth,

we think Fox might be at a house on this residential street in Norwich,

a small city in the east of England.

It's quite a narrow street.

There's not an awful lot of cover.

But unless we see him, we won't know for sure.

You're all right. We've got about three feet.

Keep going.

So now, it's just a waiting game.

All eyes are on the house.

No one wants to turn away, even for a moment. All eyes are on the house.

No one wants to turn away, even for a moment.

...