José Díaz-Balart

As a seasoned investigator, he'd learned long ago to keep his emotions at bay.

But there was something about Ana.

You put yourself in that situation of a young person with her whole life ahead of her, who came to Spain to discover another world and start a new life.

Investigators now believed that Ana's husband, David, had something to do with her disappearance.

But they couldn't prove he had driven his rental car into Spain.

None of the license plate readers in Spain had picked up David's car.

So detectives wondered, did David switch license plates so he could get into the country undetected?

The only way to tell was to get a list of all the plates that crossed into Spain the day before Ana disappeared and see if any of them had been stolen.

It totaled over 100,000 license plates.

Detective Rodriguez's team spent five weeks going through each and every plate.

Finally, they got a hit.

They discovered a stolen Serbian plate had entered into Spain through Italy.

But when they looked for it in Madrid, it was nowhere to be found.

Detective Rodriguez was exasperated, but he had a hunch.

If it was David who stole that Serbian plate, perhaps he swiped a second one in Spain and used it to secretly drive around Ana's neighborhood.

I was totally desperate.

I wouldn't stop annotating and searching for license plates.

It was the end of the workday at the station.

Everyone had gone home except Detective Rodriguez.

He scribbled down one last plate, and then, bingo.