Sounds similar to Junko Furuta murder
From what I've read about this movie, it sounds to the case of Junko Furuta. Junko was a 17 year old Japanese girl that was tortured for 44 days by 4 creeps. This happened in 1988, 3 years after this film. I wonder if the boys watched this movie and got some sick ideas from it. It has some similarities.
You can Google her name and read what these a--holes did to her!