What I'm exploring is that Westerfield did not kill Danielle per se. That he did encounter her in her room and took her away...but that she died for some other reason than her abduction.
Now, knowing he did nothing to kill her (even if he molested her, but that act may have been cut short when he realized she was deceased, hence the presence of a small amout of blood), he could not surrender to police and say, "I kidnapped her, but she expired unaccountably."
By the same token, the van Dams would not admit to giving her sleeping drugs to ensure she would sleep 11 hours and not interfere with their party.
The van Dams MUST raise the drawbridge to their personal activities to avoid concomitant actions from being scrutinized...true, they may have loved Danielle, and have they were doing the best for her, while raising the levels of opportunity for a predator orders of magnitude.
Perhaps Westerfield is betting that the van Dams will do something to deflect the spotlight of the law away from him, if he does not reveal the unwitting assistance of Danielle's parents in the crime.
Slick, OJ is not behind bars for life or facing the death penalty. And tho you are, without a doubt, solid, when you said the number 1 rule is "not to confess", IF Westerfield DID do this, and was given a life sentence or the chair, then with no way out, he MAY tell us what happened. It's not out of the question. (Wishful thinking, I know)...
sw