helene pruszynski lift by a simple philosophy, smile and make the best of everything. dding journalist did just that as she started a college internship in radio. then helene was murdered. the investigation led detectives into the darkest corners of the criminal world, before a groundbreaking investigative tool helped bring the killer's secret to light. here's josh mankiewicz with "a promise to helene". >> 40 years is a long time. that's 40 winters here in colorado. and countless snowfalls. it was on a day like this that young woman disappeared. her name was helene and helene had a friend named kimberly. a friend who kept her word. you have any idea how many years you were signing up for when you made that promise? >> no. >> for those nearly four decades, kimberly kept her promise. 40 years looking at faces. 40 years meeting with detectives. 40 years retracing helene's steps. >> when i make a promise and make a commitment i follow through. >> helene never knew it but she had another friend. you never met helene. you feel like you know her? >> i do. i feel like i know he