[TOMT][MOVIE][2000s-2010s] True crime, Mother's last conversation with murdered daughter

I have this specific memory of one scene, where the mother of a murdered girl is telling the main character about the last conversation she had with her daughter the night she was murdered. The girl had a button fall off her dress or something, and her mom helped her stitch it back on so she could go on a date. The girl and her boyfriend were then murdered, I think they were in a car when something happened. The mother said something like "The last thing I talked to my daughter about was a button".

In my memory, this was Capote, and the mother was telling it to Truman Capote, but I was reading about the case it was based on recently, and realized that this was definitely not the same crime. So it might be from the same era (2005), or also be based on a true story, and feature a writer who is close with the criminals.