>> reporter: and it was what he saw the man do that told de jong the woman was dead. >> he really slammed her. and then you don't start hiding this person in the crawl space. >> reporter: joran van der sloot is serving 28 years in prison for the murder of a young woman in peru. he's never been charged in the natalieee holloway case. now de jong's testimony seems to practically solve the mystery of what happened to natalee, and nearly ten years after she disappeared, authorities have finally got around to investigating it. >> i don't know if he's lying. i can only say that his statement can't be true. >> reporter: that construction site in 2005 is now a 12-story vacation report owned by marriott. and the prosecutor says marriott informed him at the time natalee vanished there was no construction. >> because when there's no