welcome to "dateline. " just days before halloween, joel lovelien and his fiancee, heather eastling, headed to a local bar with party-goers. the night took a horrific turn when joel stepped outside and walked into a troubling mystery. in a case filled with unknown, one thing was certain. a man was dead. police rounded up several potential suspects, but could they unmask the true killer? here's josh mankiewicz with "under a halloween moon." >> it's the one time when everyone pretends to be someone else. when being two-faced is part of the deal. >> there's a feeling that maybe the rules don't apply. and that during those moonlit hours, we all have license to eat, drink and be scary. >> halloween morphed from our national salute to sugar, into a coast to coast alcohol party. nowhere is that more true than in north dakota. several lives would collide under that halloween moon. at least one person may have used a costume to try and hide his true identity, a murderer. that weekend before halloween here in grand forks, heather eastling and her boyfriend, joel lovelien, were putting on costu