You remember when Amber said; "As soon as I learned of Scotts involvement, ummm as soon as I learned he was married to Laci."
A reporter asked the Chief if it was a freudian slip. He just brushed over it.
Hmmmmm...I wonder if, after she realized that the Scott she saw on TV was the Scott she knew, she called him and confronted him with her discovery, and maybe he said something that, while not a confession, led her to believe that what she was seeing on the TV about Laci's disappearance was not what really happened, and THAT made her call the police.