One night in October 2006, a college student needed to borrow a phone. She happened to ask a stranger with violent intentions. What makes that even harder to sit with is what investigators learned about this man afterward. There were red flags everywhere, allegations that reached back years, but none of it stopped him from being there that night.

On a Saturday morning in 1990, the body of a teenager was found on a dead-end street in the Dorchester neighborhood of Boston, Massachusetts. The scene raised immediate concerns, but the autopsy did not answer the question everyone needed answered most: how did Kasha Blount die?

A young mother disappears just days before Christmas. More than a year later, another woman is murdered across state lines. The cases seem separate – different cities, different circumstances – but eventually they converge around the same teenage suspect.