I didn't see the movie you are talking about, but another case years ago was very much like this.
A boy had been kidnapped and raised by his kidnapper as a son. Later, his kidnapper brought home a much younger boy that he had kidnapped. Only then did the older boy decide to do something. He took the younger boy and went to the authorities. I may be way off here, but I think the older boy's last name was Stanger or something like it.
About 5 or s years ago a woman and her teenage daughter and a friend were kidnapped in California, and a huge search was done to find them. Eventually their burned out car was found in the forest and the bodies were also found. I believe a female Yosemitie employee was also found beheaded. When they finally caught the killer it turned out to be the younder brother of the older kidnap victim.
This probably was turned into a movie, but this was real life events.
And it was his brother who killed the folks in Yosemite. I didn't remember if it was his younger or older brother.
The case you are talking about is the one the movie was based on.
I vote that this new case is a copycat from that movie.