Heidi visits an unlikely group of detectives: the victims’ extended family. Their sleuthing upended the police’s original theory of the case. New Yorker subscribers get early, ad-free access to “Blood Relatives.” In Apple Podcasts, tap the link at the top of the feed to subscribe or link an existing subscription. Or visit newyorker.com/dark to subscribe and listen in the New Yorker app. In the Dark has merch! Buy specially designed hats, T-shirts, and totes for yourself or a loved one at store.newyorker.com.   Learn about your ad choices: dovetail.prx.org/ad-choices