i had a coworker who's wife was killed by Derrick Todd Lee.
For months, he was the main suspect because they found her dairy about how much they fought and how much she hated him. so they.told all his family, her family their friends neighbors and everyone else he was guilty and they knew he did it, they just didn't have the hard evidence. when DNA came back from the skin found under her fingernails wasn't his, you would think they would have apologized. nope, they told him he was a wife beater and deserved everything he went through.
so even if law enforcement doesn't find any proof the parents knew, I doubt they'll say as much..