It's Gus Van Sant's fictionalized portrayal of Columbine. My reactions to it are mixed, but I want to focus on one aspect in relation to this post: Why did Van Sant feel the need for the killers to kiss each other in the shower -- and presumably more as the scene cuts out? We have implied lovers.
None of the news reports since Columbine have validated any sort of relationship between Klebold and Harris, so Van Sant added this little touch himself. Indeed all of his characters are made up (without direct 1:1 correlation to actual Columbine individuals), and yet -- there is no mistaking the event that inspired the movie.