An 11-year-old girl walked out of school and disappeared without a trace.

For years it has been one of California's most confusing and spooky cases, with many unexpected twists and strange facts.

It took 45 years to finally uncover the truth, but the story didn't end there either.

In this video we tell you what happened to Linda O'Keefe and why this investigation has captured the attention of millions of people around the world.