This is a made-for-TV movie based on the extensive undercover operation to investigate serial killer Jon Dunkle. Helen Hunt plays the role based on policewoman Lisa Thomas, who went to work at the same fast-food place employing Dunkle to befriend him and see what she could find out about a local string of missing or murdered boys apparently connected to Dunkle.
Thanks for this, FF. I just watched it. It was pretty good, even though it strayed from the exact truth regarding Lisa's involvement. I guess the film makers wanted to go for the 'dramatic ending'. Anyway, I enjoyed it.
IMDb linky: https://m.imdb.com/title/tt0107204/?r...
I learned about this re-reading The Boy Next Door.