Madeleine McCann's parents discuss new book on CNN

(CBS) - It's been four years since young British girl Madeleine McCann vanished from her family's holiday resort in Portugal in May 2007. She went missing four days before her fourth birthday.

Her parent, Kate and Gerry McCann, have now documented the toddler's case in a new book detailing their account of the disappearance.

"I suppose there's always been the urge to - to get the truth out there," Kate McCann told CNN on Wednesday night. 

According to CNN, the parents say profits from the book will be used to continue the search for Madeleine.

In spite of a huge international police operation, there are still no real leads on what might have happened to Madeleine.

Over the years, there have been hundreds of reported sightings of Madeleine, but none of them have panned out. Her parents still hope she'll one day be found alive.

On the night of May 3, 2007, the McCanns left their three children sleeping in the family's vacation condo, and went to dinner at a restaurant 100 yards away.

Around 10:00 p.m., when Kate McCann went to check on the children, she found Madeleine was gone.

The McCanns have dismissed a theory that she wandered off. They are convinced she was abducted.

Since 2007, several photos of Madeleine have been widely publicized. One shows her distinctive right eye, and another is a projection of how she might look two years on.

The McCanns say they will ask the Portuguese police to re-open the investigation into Madeline's disappearance to follow up what they say are new leads uncovered by private investigators hired by the McCann family.

If you have information on Madeleine McCann's disappearance, visit FindMadeleine.com.