I wonder if the van Dams were facing financial trouble over the past few months and were casting about for money making opportunities. Perhaps Westerfield proposed a solution to their needs (but it was illegal), and given their moral decreptitude involved Danielle. Then something went terribly wrong.
Perhaps her small body was wrapped up and went out with the trash to the landfill, but Westerfield decided to lay a false trail across the width of California and back to confuse searchers and the van Dams are playing along.
Rememeber that Pierce fellow with the Millenium Children's fund, who felt something was very wrong when he spent a few hours with the van Dams. They quibbbled over the award money he was going to offer.