MADRID—Police arrested 13 suspects as a result of an investigation done by Barcelona-based Metodo-3, an investigation agency hired by Gerry and Kate McCann to trace their daughter Madeleine, the report said.

Madeleine McCann disappeared on May 3, 2007 from her families' holiday apartment at the Portuguese resort of Praia da Luz while her parents dined with friends at a nearby restaurant. She was three-years-old at the time.

The agency's investigators were hired six months after her disappearance.

Two months into the investigation, an email came in reporting that Madeleine was featured in a paedophile video posted on the Internet, El Mundo reported.

Although it turned out that Madeleine was not in the video, the agency tipped off Spanish police who subsequently arrested the suspects in a series of raids in December 2008.

Additionally, police questioned another 10 people and seized a large quantity of computer equipment.

When questioned by AFP, Metodo-3 said it could not confirm the report.

Spain has staged a series of operations against Internet child pornography in recent years, arresting more than 1,200 people over the last five years—of whom 408 were arrested in 2008 alone.

Madeleine McCann's parents have been funding a private investigation to try to find out what happened to their daughter.

The Portuguese authorities closed their probe into her disappearance in July 2008.

AFP/Expatica