henthorn fell off a cliff. >> reporter: everyone was heartbroken for toni. harold. and, most of all, the henthorns' 7-year-old daughter haley. >> i put myself on the mountain and at the moment that she probably knew, well, this is it, you know. i know her thoughts were of haley. >> reporter: about 150 people die in national parks each year. in rocky mountain national park, the leading cause of death is falling. >> before i wrote this book, i didn't know that the national park had investigators. >> reporter: journalist michael fleeman covered the death of toni henthorn. >> i just thought the extent of their police work was to tell you to put out a rogue campfire or something, or don't park here, don't feed the bears. >> reporter: but there's more to it. every death in our national parks is investigated. and in toni's case the same emt ranger who came to rescue her now switched roles from rescuer to cop. >> people wear different hats at the park service. the guy who schlepped out there in the middle of the night and tried to both save toni's life and get harold off the