A question for those who know books, movies and/or copyright law.

I went to a movie today, based on a true story. When I got home, I looked up some info on the real situation and people, and found that some of the names were changed in the movie. Not the principals, but some of the other characters and a school.

Why? Is it something to do with permissions? Seems like if it was a true story, you could use everyone's real names and such.

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