>> i just said, is she okay? no, she died. and i fell to my knees. and my husband said, oh, my gosh, what's going on? and i said, dr. 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.