There is the academic difference that United 93 is directly dramatizing a real event while Elephant heavily alludes to but does not directly depict Columbine. Elephant is intentionally slow and seemingly aimless until the violent act, mimicking the ways these tragedies seem to spring out of nowhere while not following easy narratives, like the ones about violent music or video games that were sold to us at the time. The senselessness of the violence is also contrasted with the response to the different events; 9/11 led to the War on Terror which is still leading to bloodshed and tragedy today, while Columbine ended up just being the first major in a long string of school shootings where people are upset for a few days until everything goes back to the status quo. Because of those realities, the films end up hitting different emotional notes; United 93 came out and poked at those feelings when people were starting to doubt the wars and our strategies, while Elephant was criticizing us for our indifference and apathy to the struggles that teenagers are going through in an increasingly meaningless and empty existence. A lot of the best films about major events or moments do not try to depict the events in their totality. I have said it before, but 25th Hour is the best film about the September 11th attacks. It wasn't even formed as a response to the event, but it bleeds into a narrative about owning up to your mistakes and seeking redemption, and if anyone had dared to say that in 2002 they would have been run out of the country. One day there will be a very expensive prestige film about the coronavirus, filled with actors that make people pay attention and with a glossy trailer and marketing campaign, but it will say so much less than some small-budget drama that makes references to the event and the ways in which it drastically and subtly changed our lives.