In the fall of 2010, Roberta “Bobbie” Miller was starting over. She had a new home in Gilford, New Hampshire, she was back in school, and she was making plans for the life ahead of her. Then, on Halloween weekend, Bobbie and her dog, Sport, were shot and killed inside that home.

Judy Belfrey. Kathy Williams. Holly Davidson. Melodie Stankiewicz. Four young women whose lives crossed the same few blocks of Boston in the 1970s, and whose deaths left investigators with a pattern they could see but never fully explain.

If there is any case where you wish you could turn back the clock and change just one small decision, it might be the disappearance of Bianca Lebron. There were several moments that morning in November 2001 when a question, a phone call, or one person stopping her before she walked away might have changed everything that came next.