That is exactly the question that those of us who don't think that the state has proven their case against Westerfield would like to have answered.
There is some question that the father, Damon Van Dam, was not completely cleared as a suspect before Brenda pointed to Westerfield. For instance, Damon was known to have been driving his Blue van (possible source of blue fibers?)near the Dehesa road site, just days before the body was discovered, despite the fact that the police had ordered him not to enter in the search for the body. As a matter of fact, it was Damon that pointed the way to the searchers, asking that they search closer in, even though the area had already been searched.
And note that the body was found after Westerfield had been arrested. Where are Danielle's pajamas and her foot? Was the ground blood-soaked under the body? There would have been lots of blodd there if that is where animals feasted on her initially.